From: United States
Most of the puzzles that are released are determined by the total number of players that solve each individual puzzle every week. If you take a look at this week's 15x15 B&W PAP and compare it to last week's 25x25 Color PAP, you will see that 200 more people solved the 25x25 from last week. I cannot directly compare it to this week's 25x25 Color PAP because of the fact that it is free this week, which drastically increases the number of solves a puzzle gets.
Basically put, more people solve the Color PAPs, so more Color PAPs are released.