3 weeks? When I have used colored concrete we put color into the mix and
then sprinkled more on top, when wet. Trowel it in again and looked for any
color variations.
3 weeks seems to me the concrete will be set and the color will be just a
top coating. Which may or may not stand up to traffic.

Ask to see other installations that are a couple of years old.
--------
Yeah, ask about adding colorant to the concerete mix, and floating in
additional colorant during the finishing process. You can use the same
color for both, or go for a nice 2 tone effect.