The linear color picker crashs when you try to select the color you want.
Version : UE 4.7.0 preview 8.
Procedure to reproduce :
1/ Create a blueprint
2/ Create a linear color variable
3/ Try to change the alpha from 0 to 1 using mouse (using mouse instead of entering manually 1 is part of the procedure to reproduce). At this point, the color picker windows closes.
4/ Open the color picker again, you can still adjust the color but if you try to change the contrast using mouse, the windows will close.
5/ After trying to adjust contrast, you can no longer select color on the picker using your mouse.