American vs. British spelling for color variables

[Thibaud Colas]

This project’s Sass variables for color use the british colour spelling:

tbxforms/tbxforms/static/sass/abstracts/_variables.scss

Lines 3 to 12 in f013f22

 $tbxforms-error-colour: #d4351c !default; 
 $tbxforms-text-colour: #0b0c0c !default; 
 $tbxforms-print-text-colour: #000 !default; 
 $tbxforms-secondary-text-colour: #505a5f !default; 
 $tbxforms-border-colour-conditional: #b1b4b6 !default; 
 $tbxforms-input-border-colour: $tbxforms-text-colour !default; 
 $tbxforms-hover-colour: #b1b4b6 !default; 
 $tbxforms-focus-colour: #ffbf47 !default; 
 $tbxforms-active-bg: #444 !default; 
 $tbxforms-active-colour: #fff !default; 

.

This is to match the govuk-frontend naming, which clashes with our usual style of using American spelling for Sass/CSS variables. Our style is due to the CSS language using the American spelling for CSS keywords (background-color).