Mazda Repair: When to change ATF Fluid, 2008 mazda 3, pinkish color

Question
I don't know how many miles have been driven since the transmission fluid was changed (Automatic trans - 2008 Mazda 3) because I bought the car used.  It has 60,000 miles on it overall.  I bought it at 43,000 - and assumed the dealer had changed it before I bought it (but not sure).

I was just in for an engine oil change. The mechanic said my ATF fluid should be changed at my next visit.  He said he look at it on the dipstick.  When I got home, I looked at the ATF dipstick.  The fluid was clear with a very slight tint of pinkish color.  It wasn't "dirty" as engine oil gets.  

How can the mechanic tell I need to change it based on what it looked like?  Seems fine to my eye.

Thanks for any help.

Jerry

Answer
the owners manual will say when to change the fluid normally most cars it's well after 50000km whatever that is in miles. no machanic can really tell if the fluid is good just by looking at it. but sometimes it will have a smell to it that is different then new oil. if you trust the mechanic then have it done and never assume it was done before you bought it unless there's proff of it. when i buy a usedcar even for myself rule of thumb i change all the fluids right away