I was driving with my wife East on Toll 45 near Round Rock/Pflugerville area. I commented on all the colors of the rainbow, I’m a photographer and rainbows have always fascinated me. This one had all the colors visible with yellow right in the middle. It was bright in color, but you could still see the clouds through it. I noticed a dark object appear, literally looked like something out of a movie shape wise. I pointed it out to my wife and she saw it too. As I drove we both fixated on the dark object. The object moved to the right (South) slowly while we were drive straight towards it. It exited the rainbow went into a small light colored cloud, but didn’t exit. It appeared to cloak itself with the sky around it. It went from dark to a slow, but quick near invisible shape until we both lost it. i wish we would have snapped pics or a video, but I was driving 75mph and we were both completely fixated on what we were seeing. I’ve witnessed a set UFO (lights) a few miles West of this area, a few years ago, but this time it was daytime and the object was definitely there and definitely not any shape I could find relevance to. We live in a flight path, so I’ve seen from all angles what shape a plane can look like and this looked so large and had such a funky shape that the thought of it being an airplane instantly went away. Made my hairs stand up on my arms and neck!