Here is a sweet pea summer swatch wallet (not mine!)
Mine is the same as this, but it's marked (by me) to show which colours are best for me and at what percentage - although, tbh, I don't fuss too much about that.
I think the sweet pea description is just an indicator of the gact that the best colours for you could be found in a jar of sweet peas - lots of pinks, mauves, blues, a bit of white and red.
The aim is to wear at least three (preverably five) colours that blend together. The colour of your glasses and any jewellery counts.
I read somewhere that 'pure' white tends only to be found in man-made fabrics, so a safe bet is to assume that if it's made of cotton/silk/linen it's probably 'winter white' or slightly 'off.'
I find white really useful as an underneath layer, just showing through at the neckline. Gives a nice clean flash of brightness.
That's a good point about using slebs; I'm often left going
when told some sun-kissed, peachy type is a summer (eg Sarah Jessica Parker).
Re. the lipsticks; I came away from my consultation with a gorgeous vivid dark pink/red and a pinky/blue mauve. Was thrilled to be almost wearing red lipstick for the first time ever. A few years on and I've had to tone it down, though - was starting to look a little harsh.
Maybe you could look at the Kettlewell Colours site as a starting point?