TL;DR Summary: For your particular purposes @suntiger (building a 'dress' capsule in the same colours) I think Kettlewell should be a good match. Just be shrewd with buying less basic items & calculating your comfort levels in shipping & returning from abroad.
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I had my colours 'diagnosed' as a deep Autumn in 2019 & subsequently first bought from Kettlewell whilst in the UK (was introduced to them by the colour stylist). You can actually search for palettes on their website not only by season (e.g. autumn) but also by tonal direction (in my case, deep) if you're a little unsure of your exact grouping. The most useful thing about this is you can actually click on the individual colours in any given palette to then see all the clothing items they have in that particular colour. Could be useful for the purpose you have in mind, @suntiger.
I have since ordered from Kettlewell again here (in HK) & have found their customer service to be as good internationally as it was on home soil (even emailed them their sales team the other day to ask about the stock of a particular item, & they responded in a timely manner with a real human being lol). The only thing is shipping & returns can be a little pricey abroad, but I account for it in my calculations according to the number of items I'm buying (I will sometimes buy multiple sizes since I'm on a cusp height/ weight). I've had to do this less since the sales team confirmed that the measurements given on the website are for their garments, not the body (passing this along in case that helps you to shop better too).
In my experience, their basic pieces are the best (usually the bestsellers & the ones that are regularly restocked/ brought back in one reiteration or another over the years). I remember reading on their website that part of the reason why they have such limited stock is because they are very exact about their dye lots, so hopefully that should reassure you too.
That said, some of their more 'novelty' items can be a little hit & miss (I think I posted a review here of a satin pussybow blouse I bought from them, where the 'fiesta orange' colour looked more coral in real life). The reviews others leave on individual items often have a fair amount of information (tip: I'll often 'ctrl + f' for specific terms like '5ft3' or 'autumn' to more easily find the reviews most relevant to me).
I've gone on at length lol but I hope that helps you make a decision @suntiger. I agree with @FashIntern that the Kettlewell quiz can be a load of old tosh in trying to truly understand your own colours/ style lol. But I think if you focus more on anything that hones in on the original ethos of the company, instead of all these additional bells & whistles, you should find some fairly solid & useful basics (albeit sometimes overpriced lol) that will last you a while.