Hello .,
When I reading over your post it seemed that the main question had to do with the text with in the combo box. As for the image used for the down arrow always being black, I have submitted a feature request ( UE-18194) to the developers for further consideration.
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Hey ,
Thanks a lot, glad to see this is getting the attention it needs 
I suppose I should have worded the original question differently to prioritize what I was looking for, my mistake.
I look forward to this being implemented!
Where are you setting WHAT the text is for the items?
Hello arbopa,
The text is being set by the selected element of the combo box. I hope this information helps.
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Hello , using 4.9.2 it seems the arrow tint color is still not used. Are there any updates on this issue?
Hello haimat,
I went ahead and double checked on this issue for you. It appears that the status of this issue has not been updated to fixed as of yet. However, I will be sure to bump up the community interest in the report for this issue. Thank you for your and information.
Make it a great day
Thanks for your quick reply, . Frankly this is very disappointing, because we really need this feature. Any ideas for a workaround at least? Have you talked to your devs responsible for this, do they know some kind of workaround?
I was able to find a workaround for this issue. You will be able to find it at the link below.
Link: UMG Combobox Arrow Image not used - UI - Epic Developer Community Forums
Make it a great day
the last answer worked for me