Functional Business Rules
Business Rules should be strictly limited to expressing functional, as opposed to technical, aspects of the target situation.
For example, it is better to write "Negative amounts are highlighted on application screens using a contrasting color" than "Use #FF0000 for negative amounts". There are better places in USoft Developer to specify the actual color reference in a traceable way, and precise technical details may not be understandable to all.
On the other hand, if a customer specifies a particular color as a precise requirement, then you have no choice but to register this requirement as such, e.g. "Negative amounts are highlighted on application screens using the red color identified by code #FF0000.", although even in this case it may be preferable to formulate the functional background behind such a requirement (for example, "the same contrasting red color as in the application screens of system X") if you can.