Will color illustrations make my paperback more expensive to print?

Possibly. On Amazon KDP, a paperback with color pictures inside needs a color interior, which costs more to print. From version 1.9.22, the Illustrations card on the book's page tells you which kind your chosen style is. The black and white styles (Pencil drawing and Ink illustration) print in black ink, so no color interior is needed. Ebooks show the colors either way.