Update epic model to use new Colour DB type

What does this MR do and why?

@alexkalderimis has introduced a new Colour DB type in !81258 (merged). That was originally created on the back of a comment in the original MR that added colours to epics.

This is a follow up MR to Alex's follow up MR that updates the epic code to make use of the Colour DB type.

Screenshots or screen recordings

None

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

/cc @alexkalderimis