How to add colors to the color map in ionic v4?

Ionic Framework
1

I have many colors and redefining --ion-color-primary is not sufficient and practical.

I tried to add --ion-color-mycolor but it can’t be reached in a component, e.g. <button color="mycolor"> doesn’t work, but <button color="primary"> is OK.

Is there a way to add colors in V4 ?