Welcome back to the forum.
The rapid HIV tests, both finger stick and oral fluids, are pretty much idiot-proof -- so much so that it is possible that in the future they will be approved for use at home like pregnancy tests, i.e. without involvement of trained medical personnel. I can't comment on your description of the color dhanges, but this sounds like your OCD leading you to pay too much attention to details of the test procedure that don't matter. If the person performing the test said your result was negative, you can rely on it.
Regards-- HHH, MD