If you want the board all the same color using a transparent tint then you should do a cut lap. Laminate the tinted bottom and do 1 layer of tinted color lam on the deck as a cut lap using the bottom lap as the edge of your deck lap.
Then do a clear lam on the deck lapping to the bottom. You may want to pin line the deck to hide the cut lap...
If you use an opaque pigment all the same color you can do a free lap. Trick is to make a "master batch" of resin with the color to cover both the deck and bottom laminations, then split it and add hardener and lam the bottom. Put the other colored resin aside and add hardener when you're ready to glass the deck.