Color picking reads 3 values from a texture that is backed by 4
channels. The conversion would also convert the 4th channel.
This is a short term fix. We should reconsider the usage of reading a
different number of elements than backed by the texture. But that
requires work in the color picking and python GPU module.
Pull Request: https://projects.blender.org/blender/blender/pulls/139929
c5317faec4