Update spelling to use American English

Author: Alexey Kostevich

docs/concepts/colours.md renamed to docs/concepts/colors.md

@@ -1,16 +1,16 @@
-# Colours
+# Colors
 
 ### Usage
 
 #### Legibility
 
 Website elements like text and icons should meet accesibility standards when used against colored backgrounds. The following swatches contain a sample of each of the primary palette colors, along with recommendations for its usage and the acceptable contrast guidelines when coupled with text.
 
-## Primary Colours
+## Primary Colors
 
 The primary palette is applied across every page of the website and contains the brand, accent and neutral colors. The purpose of the primary palette is to keep uniformity across all pages while encouraging accessibility best practices.
 
-<!-- fix for styleguide selector in the colour pallets -->
+<!-- fix for styleguide selector in the color pallets -->
 <style>
   .text-xl + * {
     margin-top: 0;

docs/concepts/typography.md

@@ -6,7 +6,7 @@
 
 Text legibility is primarily affected by color. All text on the website should comply with the Web Content Accessibility Guidelines (WCAG 2.0) Level AA requirements.
 
-Please refer to the <a href="colours">Colors</a> section for more information on color contrast and accessibility.
+Please refer to the <a href="colors">Colors</a> section for more information on color contrast and accessibility.
 
 ### Sizes