I have just put "Web-safe Colours" into Google and came up with this site which seems to tie in with what you are talking about.
http://code.google.co...rty_editor_color.html
Also you could check the following.
Right click in a blank space on the desk top, Select Properties, Settings, then ADVANCED (at the bottom), General tab.
Read about 256 colours and check that you are working in 256 colours.
As long as you think your monitor is OK then you shouldn't worry about any others (unless, you see a lot more which are the same as each other but different to yours.??)