Here I give a description of a customers vehicle that we had in the shop that we didn't recommend servicing their transmission due to the color of the fluid.
Over time fluid starts to lose it's properties and doesn't dissipate heat as well and breaks down. At a certain point, though, it's too far gone and will actually cause more issues when you change out with fresh fluid. These problems occur when new fluid enters the transmission system and cleans out the unit freeing up damaged parts and causing them to wreak havoc on your system.
Let me know if you guys have found a better solution to this problem! And what you'd suggest dependent upon make and models!