I just checked the demo site and Dolphin is still using an outdated colour picker that does not have alpha levels to adjust transparency. I mentioned this a long time ago. I even did a blog about adding an updated colour picker. I am not sure if that one is compatible but the colour picker in Dolphin is a joke. Open up the js and look at the date on the code, it is ancient.
I haven't tested my colour picker with 7.4 so I don't know if it will work or not; if not, then something that will work. I posted this back in Dec. 2013 and we still have the crappy out of date colour picker. https://www.boonex.com/forums/topic/Replacing-the-Colour-Picker-on-Profile-Customiser.htm
