Varnishing watercolours?

I've nothing against White Knights (did they not use to be called Yarka?), but all manufacturers use those words, don't they?  "Extra fine watercolours using the highest grade of the finest pigment particles..." etc.  What I'm more impressed by is the last sentence - single pigments and lightfast. Our sadly late friend Thea Cable always insisted on single pigment watercolours - I don't remember if she used  White Knights or not - and her work certainly showed remarkable clarity of colour: something I have trouble with in watercolour, which has never been my main medium (and at the present rate of progress, never will be: it frustrates me, as an acrylic and oil painter, that it's so difficult to lay bright spots onto dried paint, unless one's planned the painting in detail, which I don't, or used masking fluid, which I hate).  But it's such a fascinating medium to use: can't keep away from it even though I don't do my best work in it - think I'm too 'tight', in the constricted sense of that term rather than tipsy, to get the best out of watercolour: must watch some more Alan Owen videos - he still paints every day, pushing 90, and shows on YouTube and Patreon; I see him achieve effects apparently effortlessly; doesn't quite work out when I try them.... And I'm sure he'd never varnish his watercolours!