I change the panels on my sportsbike (BMW HP4 Carbon) every couple of years just to make it look different and always take a picture of the new colour scheme and email it to my insurance company, informing them it is purely cosmetic and has no performance upgrades to the engine brakes etc. My V5 states multi-coloured and I bought the bike brand new.
They have always acknowledged the changes and accept it with no premium change but do tell me that in the event of a claim they would replace any panels with the original coloured ones only.
I do this for piece of mind as a joiner who I work with had his insurance cancelled as his transit van was black but on the V5 it was white, they wouldn't even insure him at a new premium even though he had been with them 20 years and never had a claim.......
I don't understand the ins and outs of the reasons but wouldn't like to give them the chance not to pay out if the worst happens due to non disclosure. Could be the best £25 you'll spend this year, it's not even a tank of fuel.
I'm sure some guys on here work in insurance and can explain what to do for the best.
JimmyMac