The colors of the crayons absorb different wavelengths of light. Dark colors like black and purple have the shortest wavelengths while bright colors like yellow and red have the longest wavelengths. Blacks and purples absorb the most light and therefore, the most heat. That’s why you get so hot when you wear black in the sun! That’s also why black cars heat up the most on the inside. That means that in the oven, black and purple crayons would get the hottest and melt the fastest.

It probably doesn't matter, but if it does then it would depend on the dye used to make the crayon and how much of it there is. The dye determines the color, but there are probably more than one dye that make the same color. This means that without knowing what dyes were used to make the colors, I couldn't tell you.

You can find out yourself though if you try it!

The melting point of standard crayons are pretty much the same, as they are made of the same material paraffin wax. The pigment is added for color, and it doesn't affect the melting point of the crayons.