I pressed tulip petals a few years back. Mold was not a problem, but the red, purple, and deep pink tulips came out blotchy, with transparent areas where the pigment had seemed to leach out of the petals. The yellow tulip petals dried well with no blotchy parts, though they started discoloring to brown and tan within a few months of being used in a picture. Overall, I was disappointed with the results.

It might be worth it to try a microwaveable flower press - possibly the fast drying will eliminate the mold issue and preserve the colors more uniformly.

kms