Hi there,
A RIF is one that is realistic, whether that be black or tan it is deemed to be almost indistinguishable from a real gun. The brightly coloured IF's are over 50% a bright colour as prescribed by the HO that might be orange, red, green, blue or clear. You only need to be over 18 to buy one if these as thy are considered imitations and not realistic due to the aforementioned colours.
If I was you, I would wait until you can get your site membership sorted and buy a RIF. Second hand sales of bright IF's aren't the easiest and lose a lot of value.