customisation of process steps – white background issue

Hi,
pretty simple really, I have the process steps on a white background and the background within the border is also white (so the line behind doesn’t show). This is all fine, but when the cursor is hovered over the process step, the central icon turns white and can’t be seen.

I have found where to put the horizontal line that links the steps behind them and where to change colour and size of said line, but I can’t find the CSS that controls the icon effects and since it is integrated into the process step I am confused as to why it behaves differently. Anyway I just want to keep the icon the same colour and maybe put an outline/shadow during hover rather than change the icon colour.

thanks in advance

Luke