Very popular bike at the time, a couple of my friends had them, the RD400 was sporty, fast, and handled well. Almost every one I saw was blue, but other colours were available.
There was another version of the bike, the 'Daytona Special'. Sold in the US but not the UK, this had different styling, an engine with a 'ram air' head, and (I think) some sort of exhaust valving to reduce pollution. I'm not sure of dates, but I think we got the watercooled RD350LC instead.