Sigma 17-50 Yellow color cast.

Wouldn't light theory suggest that using a yellow filter on yellow light, the result should be whiter or brighter? Trouble is that is complicated by the less even exposure across the range I see with third party lenses. The one on top right is the dingy look I tended to get from Sigma, but the bottom left is the brightest one.

If anyone wants to really get into this, there are daylight bulbs available.