Where do white chia seeds come from? The exact same plant as their black seed counterpart: Salvia hispanica. The only difference between black and white chia seeds is a single recessive gene, which produces the lighter version. Seeds from both are cultivated, though the black version is much more popular.
As far as antioxidant content, both version are quite high, however black chia seeds testing has shown it to have an ORAC value 40% higher than white.
Research Support, Non-U.S. Gov't: ChromaDex Analytics White Chia Seed Sample Report (PDF) Mar 2006