It looks as the blue channel is not considered as empty (thus substracting it gives yellow).
There are inline procedures so there may be a problem of linking. Try to remove lib directory of bgrabitmap.
I do not know if it is inside or outside ClearTypeDrawPixel. If the problem is inside this procedure, then if you call ClearTypeDrawPixel with Cr,Cg,Cb equal to 0, then you should obtain yellow color on white background. If the problem is outside, then if you replace line 886 of BGRAText.pas, in BGRATextRect procedure
BGRAFillClearTypeRGBMask(bmp,lim.Left, lim.Top, temp, c,tex)
by
BGRAFillClearTypeRGBMask(bmp,lim.Left, lim.Top, temp, c,tex,false)
You should obtain instead a cyan background.