Complex sentence: The universalist side claims that our biology is all the same, so color terminology development has absolute universal constraints--while the relativist side claims that the variability of color terms cross-linguistically points to more culture-specific phenomena.
Split into simpler sentences: The universalist side claims that the biology of all human beings is all the same, so the development of color terminology has absolute universal constraints. The relativist side claims that the variability of color terms cross-linguistically (from language to language) points to more culture-specific phenomena.