Personally I wouldn't paint the parts as the blue will start to show though when the painted parts get dinged and scratched through normal use
Urgh, tell me about it, by the time I pulled the trigger on buying an XR-5, I could only find it in DayGlo Blue, and the paint and varnish keeps wearing through on the rub points. I'll likely just start taping over it.
Thomas, the
legal position is that it's a strict liability offence to modify a non-realistic imitation firearm into a realistic imitation firearm, even temporarily, in private:
https://www.legislation.gov.uk/ukpga/2006/38/section/36
However, it's a
defence to do so for the purposes of playing airsoft at a site with 3rd party liability insurance:
https://www.legislation.gov.uk/ukpga/2006/38/section/37 as amended by
https://www.gov.uk/government/publications/the-violent-crime-reduction-act-2006-commencement-no-3-order-2007-firearms-measures
There's no age limit on the defence, or particular criteria to claim it. The UKARA-style 3-games-over-8-weeks scheme providing the level of evidence that retailers considered necessary. You can make your own decision on it.
Practically speaking, it's only going to come to the attention of the state if you do something silly with the gun out in public. At that point, Firearms Act 1968 Section 19 applies, and it doesn't matter if it's a realistic imitation or not. Since you already have the gun, and haven't gone on a rampage with it, I think you can be trusted not to do so if it happens to get blacked out.
However, I'd agree that the lowest risk option, particularly while you're under 18, is to use sniper tape, which comes in solid colours or camos. If you tape up on site then remove it at the end of the day, then you're satisfying the letter and the spirit of the law.