The global color and opacity of assistant tools are not saved to .kra file.

Steps to reproduce:
1) Create new document
2) Create two assistants somewhere
3) Change the ('global') color and/or opacity of one of the assistants, then for another use "Custom color" and set the ('local') color and opacity
4) Save the file, close, open again

Actual results:
5a) The assistant with the local color looks the same as before reloading; the assistant with the global color returned to the default color (light grey) and opacity (100%).

Expected results:
5b) Both assistants have the color and opacity set before saving, closing and reopening the file.

There are two workarounds:
1) Choosing a custom color for every assistant tool - but it is time-consuming and choosing a color once would be better; also the default color of the custom color doesn't change to the last used, which contributes to the time-consumness (and annoyance) of the solution
2) Changing the global color every time after opening a file - still, choosing a color once would be better