If I search something on Google Images, multiple boxes appear with similar ideas. These boxes are in different colors. Why? Wouldn't it look nicer to have one uniform color?
These are an attempt at differentiation by type of suggestion for search refinement. It's early days, NLP is not a science, and barely an art.
Which colours to use is a more interesting question, and whether or not shape, size and spacing would make better differentiators is also a valid question. There does need to be some form of differentiation between the types of suggestions they're offering.
This might be an inspired copy of the colour "system" pinterest uses for a similar effect. Which was probably copied from somewhere else.
The question you've asked of google is interesting because the suggestions they're giving for further refinement of the question all look very similar in type. If you ask a question with very disparate types of possible refinement the colour differentiation might make more sense.
I think it's early days in whatever google is doing here. Notice how there's no "exterior", "interior", nor more of their range, or things like context. e.g. where's "racing", "advertising", "lifestyle" or other types of imagery associated with a brand such as this.
What's strikingly peculiar is that gtv8 is correctly grouped with modified versions of Alfas, despite being a really rare and esoteric thing. That it's here at all is odd. Probably a reflection of my surfing history ;)