You can colour it whatever you want. I just copy-pasted the green one a couple of times and changed the colour**. I just wanted to make sure people knew that, as most custom control sets available on the Tools Network are based on PNGs, which cannot be recoloured (and don’t resize well either). I’m trying for resizability and recolourability. I include the “Google style” checkbox, because it is nice and fits well with other Google Icons, but it is not resizable or recolourable, unless you manually swap out the icons with new ones from materialdesignicons.com.
**Note: it’s slightly tricky to change the colour, as the checkmark’s invisible containing box blocks the colour tool from affecting the box underneath, unless you click near the edges. Unfortunately, the checkmark isn’t recolourable (it’s a vector graphic imported from LibreOffice).