How can I change color of an Image in script (png source) ?

I made a png image with gimp with one color and transparent. I have include this image in Image UI component in unity. I linked my image to my script, as usual.
143868-variable-declaration.png
But I find many ways to change the color on many forums (mainly answers.unity) but none of these work in my project :
143869-assignation.png
I know the first one is only if I declared my image as gameObject.

How can I do the color change ?

Thanks to @Casiell for the answer. Thanks to @SirPaddow too but I don’t try the the sprite.

In the case of peoples can’t read the comments, I put the answer here :
144073-answer.png