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I'm not sure about spears particularly, but there's a major tendency to paint everything in much of the period, including weapons.

We do have evidence for pole weapon shafts being painted - several of the surviving examples have traces of paint remaining. Red seems to be quite a popular colour, but I've seen a couple of black ones, and a green one, in the Royal armouries and the wallace collection.

Some of the pole weapons also have shafts covered in fabric, usually velvet - these are mostly c16th, but I can't see any a priori reason why you wouldn't be doing this in the c15th.

Lances for tournament are certainly painted -you have two surviving lances in the Royal armouries, both painted, and several descriptions of tournament lances as being painted.

Where they occur in art of the period, war lances are most often brown (more than half), either as a paint or natural wood colour, with red again being second most common.

Some have quite elaborate designs, eg the lances illustrated in the Lady and the Unicorn tapestries in the Musee de Cluny in paris are mid-blue, with a pattern of white crescent moons running up the shaft.

Hope that helps