Well done, Richard, good attitude.
I needed a career change at age 54, (from a healthcare related profession), managed to get a 2330 place at Swindon, one day a week, and eventually enough agency placements (as a mate, of course) to learn the mechanics of the trade. Like you, also had extensive DIY experience which included various facets of construction besides having electrical and electronic knowledge.
It worked for me, and having passed 17th & 18th Edition tests (and an AM2, which they told me afterwards that I didn't actually need), I ended up in a super maintenance job that included a fair bit of new install. In retirement, I still do it on a voluntary basis for my favourite local outdoor activity youthwork charity.
Coming onto the trade as late as I did, it remained 'fun'; had I been doing it from age 16, I'm sure I'd have had enough by now.
I think other comments above may be useful; my strong preference is for industrial/commercial rather than domestic, for a number of reasons that include the above.
Regarding your colour vision issue, I suspect it might not be as great a bar as you fear. It's very important to know that there's a world of difference between 'colour defective' and 'colour blind'. Colour vision deficiency can be regarded as a 3 dimensional space, with normal colour vision represented as one small area within that space. How far away from that area you are, can be determined by a number of quantitative tests. Your optometrist should be able to help if he/she is any good (and if not, find an Independent one rather than one of the national/local groups); they will be able to refer you to the optometry department of Cardiff University for a further opinion if they can't advise fully themselves.
Hope all that helps.
Graham