Need to remove hard-coded instances of blue

Hard-coded instances of blue in the confluence stylesheet override user-specified colour schemes (and look terrible). This means if a user specifies their own colour scheme, it only "mostly works". This has knock-on effects for developing new themes.

Fixes for this issue will include a combination of...

• getting the appropriate user-specified colour to apply
• changing the CSS so it simply inherits the right colour
• changing the override so it sets a reasonable neutral colour (usually black, white or grey)