Hi Asgeir,
Edit: I assumed you had tried changing Member to value in your rules. Typically that should let you do what is needed but if not then I covered an alternative recently in my series on MDX, in part 4 - Scroll down to the middle where you will quickly pickup on the glaring red, green and yellow.
If you have positive and negative values and want to check based on an ABS() variance, there is no ABS() function in TM1 MDX. You could try square the value then square root it again. And there is no SQRT() function so you may need to do (([member]^2)^0.5)
Recently someone reminded me too of Declan's video on YT where he shows something similar.
Also, keep in mind that the later versions with the new Format Manager works more intuitively with conditional formatting and may be an option:

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George Tonkin
Business Partner
MCI Consultants
Johannesburg
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