Creates a pixel pyramid with separate uniform colors for the cubemap-Y faces.
Usually, this method is used to create a pixel pyramid that fills holes at the North and South poles (e.g. Mercator voids).
The size of the bottom-most pyramid level, in pixels. Will be round up to the next power of two.
The uniform color value for Face.NegY. This is usually the North pole.
The uniform color value for Face.PosY. This is usually the South pole.