Click on FORMAT
Then click on FONT
You will get a box come up on screen.
You will see three drop down menus. FONT COLOUR, UNDERLINE STYLE & UNDERLINE COLOUR.
Click on FONT COLOUR
Then check the STRIKETHROUGH BOX - this will allow you to make the font & strikethrough the same colour but I am not sure you can actually change the colour of the striketrough by itself. I have just given everything I know a go and failed. - I will keep trying for you. If I find out it's possible I will let you know ASAP.
You can however apply an UNDERLINE by clicking on the UNDERLINE STYLE drop down menu and then apply a different colour to that by clicking on the UNDERLINE COLOUR drop down menu.