Sorry, I could not reproduce this issue on Win10 Pro BSS 2.7.0.
I dragged a hero component in, selected the paragraph area typed in #fff in the Bg color field. Then clicked the color square and from the popup I selected a color value. Then clicked select and the Bg color field updated to have the hex value of the color selected in it, not #fff.
Thanks for looking at this for me. I shut down BSS, hoping it was anomaly that would clear up, but no. Here's a picture of what I'm dealing with.
Changing the color to Blue using control A works...until I press Select, then the preview reverts. As you can see, the selected box is Green in the preview, but both color controls (A and B) are set to Blue. If I use control B to change the color of the Box then the change sticks.
I tested changing more attributes in the element.style section of the Styles panel and see the same sync problem. So the bug must be in the "confirm updates in Preview" routine for this only.
Sorry still can't really reproduce it, I used the same component you have in the screenshot.
I thought I might had once I edited the CSS block for the box class then edited the inline style then did an undo where all the code reverted but the preview and the little square remained as the previous color, but once I just selected Select again it all reverted back. That seem to be only time anything like what you described happened but was solved by selecting Select again.
Just as a side note, you really should be selecting the Style Attribute drop down and selecting the CSS block of that element or if you are making different boxes different colors use the create block option and then update the CSS that way rather then using inline styles.