Chemical Analysis
The Big Questions for Brake Fluid, Coolant, Gear Oil and Engine Oil Analysis : 
Is the time to change the fluids in your machine based on the color of the brake fluid, coolant and oil?
Is it based on the operation time or non operation time of your machine?

Discoloration of these chemicals isn't necessarily a reason to change them. Chemicals can easily be discolored by components in the system. Analyzing the expiration of these chemicals in your machine makes it much more cost effective to pin point what needs to be changed. It also saves internal components from being damaged by focusing on the area that should be addressed. Using these methods proves that some chemicals don't break down as soon as the manufacturer states and that the expiration is inaccurate. These expirations are measured in percentages as recommendations, not specifically of the individuals riding habits.   
          Head gasket and base gasket failed internally 5,000 miles.

This is rare. I've only seen this once. There were no signs of external leaks around the head gasket and base gasket. It passed a compression test and a leak down test. It even passed a pressurized cooling system test. After taking pictures inside the combustion chamber, the problem still didn't reveal itself. After removing the head, I found the head gasket failed at the stud. Weird! Then coolant ran down the stud to the base gasket. Making the base gasket fail, then contaminated the crank case with coolant. 

I knew from the beginning coolant had contaminated the oil when I drain it, but I had to prove it and find the leak. Sometimes, even when you have all the cool diagnostic toys, there's nothing like a visual inspection to solve the problem.      
  Oil contaminating the coolant.
coolant with zero contaminates
Brake Fluid
Brake fluid has the shortest expiration of all, but it doesn't absorb moisture as quickly as you think.  I have been told in the past from numerous colleagues that  once a brand new bottle of brake fluid has been opened,  you have a week, maybe two before it expires. Some brands of brake fluid ,new in the bottle, contain 1% of water.  In an open unsealed container, after 8 days I tested "dot 4" brake fluid in the middle of the rainy season, and to my surprise I found it only contained 2% moisture.  



Clearly for safety reasons, it is important to flush the brake/clutch system if the moisture percentage is too high. Water has a much lower boiling point allowing the system to fail.  It also preventively saves components in the system from wear and being damaged, which keeps the cost down.  Brake fluid with a high percentage of moisture begins to corrode the system, creating an abrasive material similar to sandpaper.  It's much cheaper to bleed the system than to rebuild calipers and replace damaged master cylinders and clutch slave drives.      
Brake fluid with 1% moisture 
acceptable
That being said, depending on your location and riding habits, without testing the purity of the brake fluid, it's hard to tell when it is really time to flush the system.   
Brake fluid with 2% moisture acceptable 
Coolant
Coolant by far has the longest expiration.  A standard recommendation for flushing the cooling system is every two to five years. This is assuming the coolant pH is at the correct value between 9.5 -10.0.  If the pH is below 8.3, then this is not acceptable for engine use due to its corrosive nature. When the pH is too low, the acidity level is too high and the system must be flushed.  This can damage, destroy and deteriorate components in the cooling system such as: the water pump, thermostat, cylinder water jacket, head gasket, seals, o-rings and coolant lines.         
brake fluid with 3% moisture
ready for a system flush 
brake fluid with 4% moisture
definitely needs a system flush

Oil
I am not going to go into great depth in the topic of oil. It is a touchy subject. Use what works for you. I believe what oil to use in your bike is opinion and preference. Read your manual to see what is recommended. Professionally, over the years I have seen the outcome of certain brands. I highly recommend buying engine oil, gear oil and 2 stroke oil from a motorcycle/scooter shop or online motorcycle specific website. It's not worth the risk trying to save a couple of dollars cutting corners. The outcome later could end up costing you much more.
The oil service is the most important. Oil is the blood that circulates in the engine, which cools, cleans and seals internal components. It is important to use the recommended weight oil for your machine.  Oil viscosity does change with temperature.  Performance can be affected depending on your environment, climate and the different seasons when your riding.    
        Zero clutch cable free play.
oil is two years old with 4,300 miles.
Under normal circumstances, in a wet sump 4 stroke system, contaminants in the oil come from: carbon being scraped from the cylinder walls, breakdown from the clutch friction plates and normal friction break down from internal components. These substances are constantly being circulated through the system, allowing the oil filter to capture these foreign particles.  When the oil filter is full, these particles continue to circulate unfiltered.  At this point, it is time to change the oil.      
How do you know when it is time to change the oil?  Does it depend on mileage or time? 
If you have a keen sense of smell, unscrewing the dipstick or smelling the exhaust to see if it smells burnt will give you a pretty good idea when it is time to change your oil.  If you ride under a thousand miles a year and change your oil yearly, you might be throwing money away. The only concern you should have with oil that has been sitting in the engine or oil with low mileage that's a year or older is moisture.  This is where I come in.  I can test the oil expiration for moisture and metal particles. 
Sometimes I find people change their oil way over it's expiration. A thousand miles later they need another oil change because the residual oil from the previous oil change still remains in the system. If you do the oil change yourself, make sure you change it right after a ride, or at least start your bike up and let it idle for 10 minutes.  This brings your bike up all the way to operating temperature before changing it. You want all those foreign particles suspended in the oil, so when it drains, it is all flushed out as much as possible.  

                     Caution: the oil will be extremely hot! 
Coolant contaminated the oil
Feel free to bring me a sample of your oil, gear oil, fork oil, coolant and brake fluid and I'll check it out.