I feel that this word is not quite right. The word "Ru" is usually followed by a noun, which means "like ……", but the most common meaning of Hong is used as an adjective, which only means bow sound, so the word is "like bow sound", but I have never seen this usage.
But both "as red" and "as red" can be explained.
"Like a flood" is like a pool of water.
"Like a rainbow" is common in "Like a rainbow", which means that the momentum is very strong and seems to run through Changhong.