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UMG Widget color and Text color has different color output at UE4 editor to Mobile preview and Mobile device.
1. Create Widget BP.
2. Added Text and button.
3. Changed Color.
4. Next Play Mobile preview button and deploy contents to device.
5. Check different color output.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-18154 in the post.