There are three colours, and each does a different job in your shop. Worth knowing which is which before changing them.
Configurations › Online Catalog › Display Options
The first three options are Main Color, Secondary Color and Background Color. The dot next to each shows the current colour.
Main Color — your brand identity. It paints the active category, the selected variant, the filter chips and the navigation highlights. It's the colour customers associate with your shop.
Secondary Color — the conversion colour: product prices, the add-to-cart button and the checkout button. It's the colour that drives the sale.
Leave it unset and it inherits the Main Color.
Background Color — the background of the catalogue's pages.
Tap the colour you want to change. The picker opens, where you can:
#34076D).Tap Select Color. The change saves right away.
If you see this in red:
"Low contrast between secondary and background colors may make prices hard to read."
It means the secondary and background colours are too close. Since the secondary colour is the price colour, customers will struggle to read what things cost — and a price nobody can read is a sale that doesn't happen.
Typical cases: pale yellow on white, mid grey on light grey.
The fix is simple: darken the secondary colour, or lighten the background. The warning disappears on its own once the contrast is enough.
Use the Main colour for your brand — the one on your logo, your sign, your shopfront.
For the Secondary, pick something that stands out from the background and appears nowhere else on the page. It's the one that has to pull the eye to the price and the buy button.
And resist a strong Background Color: white or near-white lets your product photos do the work, and the photos are what actually sell.