The worlds color variations are a first pass where some colors were reused. In the longer term there will be more color variation available.
Items and blocks have up an 8 bit (256 possible values) color index in to a color palette. There are various palettes that are for families of items/blocks so when you crafted an item the color index of one of the inputs is passed through for the item color (where its used).
The index is why the color mixiing thread wont fully work as there is not storage or a full 24 bit (or 16 bit) rgb to mix. We have discussed paints/dyes to allow items to be colored for a reserved set.