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My research led me to conclude that you have discovered a bug. VBA fails to read the DisplayFormat in a UDF. It's a pity, since you invested so much time and effort into your concept.
In the attached workbook the work flow is to enter something on the MEI tab. If the entry qualifies the cell colour changes. There are many of your excisting entries. Just select any of them and press F2 (to enter Edit mode) and Enter. This action also changes the value of the related cell on the Uang tab. The formula existing there will be over-written. The code also changes the colour of that cell. Please remove the CF because your CF over-rides the colouring set by the code.
When you activate the Uang tab all totals in columns AU:AW are calculated. That means that those totals may not be up to-date when changes are made in MEI. If you look at Uang, go back to MEI and make a change, Uang totals will not reflect the change until you look at it again.
All colouring is done to match Uang!AU:AW, both for fill and font. The font colour is not considered in the SumByColor function but you don't see many totals there because most of the colouring in Uang is done by CF.
Look for the code in module TXL_5438 and in the code modules of MEI and Uang. I tried to keep the code simple and transparent but if you needf any explanation please don't hesitate to ask.