color-literal
A color literal stands where only a named color is allowed.
A color such as #123456 is allowed only as the result of a phrase with no holes, which gives the color a name. Everywhere else write the name, such as theme.Accent.
Example
Check this program to see the diagnostic.
# package p
define Sky [n: number]
result #123456
Diagnostic
p/p.synod:3:10: error[color-literal]: a color literal stands only as the result of a phrase with no holes
hint: name the color, as theme.Accent does
Fix
Remove the holes, so the phrase names the color.
# package p
define Sky
result #123456