theme.accentColor

One color; the hover and subtle shades are derived from it with color-mix, so you do not have to supply the family. Leave it out to keep the SDK's indigo. Set as inline custom properties on the viewer's root element (.ks-viewer), which is why it is per-viewer rather than global. Any CSS color (#e91e63, rgb(…), oklch(…), color-mix(…)): a hex, a name or one color function. Anything else — a value that is not a color, or one carrying more than a color — is ignored with a console warning, and the indigo stays: the color is written into a stylesheet, so only a color may reach it.

theme: { accentColor: '#e91e63' }