From my experience with law, including university lectures, the only part of law you can be charged against is an Act of parliment, such as the vcrA. I have read the act, thoroughly, and that is all that a prosecutor can reference in any charge against you. Regulations are essentially extentions, so what you have quoted is a guideline, not a law.
Besides which. It only offers one way of making an IF. Did you even read what you quoted? It states that a gun not of these colours is not automatically an RIF, but it depends on How realistic it looks