transmission shifts smooth but why is fluid kind of dark?

newly acquired 08 mazda 5, 120k miles. it shifts fine, no hesitation or slipping. did 2 drain and fill in the past 4 days but fluid is still dark after test drive, does this indicate potential issues?

pic1 is taken right after test drive. after 5 mintues, the darkness seems to go away, pic2 is the sample fluid but minutes later.

I used castrol IMV.

What fluid are you using?

Drive it for 2 weeks, then do a third drain and fill. Then do another one in a year. You in all likelihood have zero issues. What can happen is new fluid can get discolored as it is dissolving old build up tarnish. Once that is all gone, your fluid will stay red, if you stay on top of the changes.

The automatic transmission case typically holds ~8.5 quarts but drian and fill only takes away 3 about quarts. Even if you drain it all, there's residual oil in cavities and place you can't clean without tearing it apart. Don't need worry about color. If it shifts good, it's good. FWIW, once you drain and replace all of the motor oil, it turns dark almost instantly.

If you really want to know if there's a problem, you can send in a sample for an oil analysis ($25 black stone labs) if you want a piece of mind.