Since vellum is some what transparent, you should always start off by making some sort of background. Here, I used a simple stamp white two ink pads; the multi-colored one and a silver ink pad. The multi-colored ink pad helped a lot since I didn't have to worry about blending in colors. It gave the card a very nice rainbow effect.
Stamp your pattern on the vellum using a black in pad. Set it aside to dry. The time that the ink takes to dry really depends on the kind of ink pad you use. There is a kind of chalk ink that is mostly used on vellum because it dries instantly, but this time, I used a regular black ink pad, so it took a good five minutes to totally dry on the vellum. Make sure that the ink is dry before you start working on it, because the last thing you want is to ruin a good piece of vellum by smudging your pattern...