I bought a mistint paint (Pink with a slight brownish hue)
I mixed in alot of white paint (the shade of white was called Bistro White) that I already had to lighten it up, almost 50-50.
These are both the same brand gloss (Valsper Signature Paint + Primer Satin).

I did half the room one day and the next weekend finished the other half... all looked fine at this point.
But then the next week I did some touch up painting on spots where the old paint was poking through and for some reason the paint came on a slightly but pretty noticeable color... sorry i didnt take pics before I left but I'll describe it as a faded color with a more whitish-blueish hue to it.

Before I painted this touch up coat I mixed the paint just as well as I did from the previous times using a drill attachment. I used a new roller and roller tray too.
Any ideas of what could have caused this? thanks

 

My daddy was a painter and he would tell me that some paints you could "patch" (touch up) easily and others you had to paint an entire wall (or whatever) because the patch would always show. Sounds like you have a paint that is just not forgiving of touching up.

 

I agree ..... unless you didn't mix the 2 colors as well as you thought you did. Another possibility is you didn't get full coverage allowing some of the previous color to bleed thru and the touch up got complete coverage.