You can't set a specific color any field or measure ,Yes what you can do you can set to multi color but you can't set as red is for field 1 or by your choice it will be set by automatically or you can set color by values i.e less than 100 will be red , above will be green.
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As mentioned by gwassenaar using if or pick match statements in color by expression.
You can set a specific color to any dimension member of the Chart i.e if you have Branch as field and North,South,West,East as values you can set each one different color.
if you have 2 measure as Actual and Budget then you can create a dimension by using Valuelist as Valuelist('Actual','Budget').
In Measures Section Use it as pick(wildmatch(Valuelist('Actual','Budget'),'Actual','Budget'),sum(Filed_For_Actual),sum(Field_For_Budget) )
In Color by Expression :
I hope this is helpful.