Silicone muffin molds are perfect for creating colorful gelatin desserts.
Find a mold that you like and fill it with a color base of your choosing.
You can use a color base with milk for an opaque texture of add a bit of color to a water base to create transparent sections.
Plastic chocolate molds work well for gelatin too:
Let the gelatin dry a little bit in them. Once the gelatin edges are starting detach themselves from the mold, pull the gummy shape gently and you should be able to remove it from the mold without ruining it shape.
Another way to make color base shapes is to let the base set in a larger container and then cut the desired shapes out with a knife or a cookie cutter.