When pressing alt and releasing, PyxelEdit activates the top menu (file, edit etc.) and changes the mouse pointer to standard win mouse pointer. So if I want to pick a color but change my mind I need to click in the editor to go back to whatever mode I was in, though it seems that only the pointer changes and not the actual mode because when I click in the editor the program still perform the action of selected mode (for example it draws a pixel before the pointer goes back to normal).
I don't know if I explained the problem good enough but it's easy to recreate. Just press alt while pointer is in editor.
:)