The filter is usually good to go if just cleaned. You change the fluid to get a new dose of detergent additives to keep the tranny all [censored] and span inside, which it likes a lot. Our trannies make a lot of heat, and heat kills the life of atf, so annual fluid changes are not a bad idea. That said, how many trannies belong to folks on here who have 50k miles on the fluid, or more? I bet more than a few, and the boxes just keep on running and shifting and running and shifting...

As to the colors, red means new, light tan means older but ok, dark brown means change me now, burnt smell means change me now and find out why I stink, like a pressure test and drive test...