Excluding Value Combinations in VC

My task is to to prevent a black hard case from being paired with a pink soft case. Also, I have to prevent a white hard case from being paired with a black soft case. Aside from those two exceptions, any other hard case can be paired with a different bumper.

For starters, I went into a dependency I had created. It was called "HARD_BUMPER." For syntax I tried:

IF HARD_CASECOLOR = 'BLACK_HARD' NOT(SOFT_BUMPERCOLOR = 'PINK_BUMPER'

NOT (HARD_CASECOLOR = 'BLACK_HARD' AND SOFT_BUMPERCOLOR = 'PINK_BUMPER')

The second one passed the syntax check, but it had no noticeable effect. I was still able to pair the black hard and pink soft in the sales order. The first one didn't pass the syntax check. Ultimately, I deleted both of them. Am I on the right track? Or, should I try something different?

A few words on the scenario:

We are manufacturing Iphone cases. One part of the material is a hard case. The second is a soft bumper. The scenario works fine going through a sales order. I just have a new requirement (banning certain hard/soft color combinations) that I am not familiar with implementing.

If any help could be offered, I would appreciated. This is my first post, so I look forward to hearing from you all.

P. Kaushal