1. What a tool will and will not do for you
Worth establishing before the advice, because this genre routinely blurs it. Saving a brand kit means your colours, typeface and logo are applied to everything you make afterwards, which removes the hex-code fiddling. It does not evaluate the result. There is no contrast checker here, no alt-text field, and nothing that measures or certifies accessibility — so if your brand accent is a pale yellow, every sheet will faithfully render text nobody can read. Everything below is a check you make, not a feature you switch on.
2. The 60-30-10 proportion
A common failure is using too many colours at equal weight, which leaves a reader with no idea where to look. A workable starting split is roughly 60% of the sheet in a neutral ground, 30% in a structural colour for cards and headers, and 10% in a single accent reserved for the figure that matters. The specific numbers are not sacred; the discipline is. One accent, used once, is what makes a number look important — the same accent used nine times makes nothing look important.
3. Contrast ratios, and why this is the part to measure
The Web Content Accessibility Guidelines set 4.5:1 as the minimum contrast between body text and its background at AA, and 3:1 for large text — roughly 24px, or 19px bold. These are worth knowing because they are the one part of visual design with an actual number attached, and because a sheet is often read on a phone in bright light, where a combination that looked fine on your monitor disappears. Any free contrast checker will give you the ratio from two hex values in a few seconds. Do it before publishing, not after somebody tells you.
4. Colour cannot be the only signal
Around one in twelve men and one in two hundred women have some form of colour vision deficiency, most often affecting red and green — which are, unhelpfully, the two colours everyone reaches for to mean bad and good. Never let colour alone carry the distinction. Add an arrow, a plus or minus, a distinct line style, a direct label on the mark. This is worth doing even for readers with full colour vision, because it also survives being printed in greyscale, photocopied, or screenshotted at low quality.
5. Colour associations are real, and weaker than usually claimed
Blue reads as institutional and steady, green as growth or health, red as warning or loss, at least to readers used to Western business conventions. That is worth knowing and worth using, and it is a much smaller effect than colour-psychology articles suggest — nobody trusts a report because it was set in navy. Choose colours that do not fight the content, then stop thinking about it and spend the time on what the sheet actually says.
6. A practical order to work in
Pick a neutral ground first, light unless there is a reason. Choose one accent, and check it against that ground with a contrast tool. Give every other element a greyscale value, so the sheet still reads with all colour removed — if it does not, the layout is relying on colour to do structural work. Then add the accent back in one place. A sheet that works in greyscale works everywhere; one that only works in colour is one bad projector away from being useless.