Portals; New tags to retrieve Theme colours based on whether they are deemed to be dark or not

The following Theme Tags have been added for Portals:

• ContrastColourDark
• ContrastColourLight
• MainColourDark
• MainColourLight

These dynamically return either a dark or light colour based on an algorithm which checks the background colour, i.e., ContrastColourDark will return ContrastColourBackground if this is deemed to be a "dark" colour, otherwise it will return ContrastColourLight.

These tags can be used to avoid situations such as showing white-on-white text.

NOTE: These tags use a special algorithm to determine whether a colour is dark or not and are not designed to pick the "darkest" or either the foreground or background colours but rather to pick a dark colour or the lighter of the two colours (depending on the tags used).