well I am not able to find a plant with the common name rainbow flower other than the Iris named after the goddess of the rainbow. this clearly isn't an iris.

So what did the advert say when you bought them and was there a picture of them?
these look like some type of sunflower/Rudbeckia/ helianthemum.

Some variety of Rudbeckia hirta. Still a pretty flower, but nothing rainbow-ish about it. Palette in the cream-yellow-orange-rust-brown range.

A lot of seeds on Amazon and eBay have multicoloured photo shop pics that don't relate to the plant. It's to make you buy it. In fact i wouldn't use anything from China or Russia eastern block type. Most don't germinate