I use these colours myself, set by mIRC Address Book (Tools Menu -> Address Book) or ALT+B
~ Purple / & Yellow / @ Red / % Green / + Blue - and after 10 mins of inactivity, They turn dark colour
Or search for cnicks in mirc.ini and replace with this:
(remember to go into Address Book and tick Enable so they show up)
[cnicks]
n0=,6,~,,0,0,0,2,10,0
n1=,30,&,,0,0,0,2,10,0
n2=,5,@,,0,0,0,2,10,0
n3=,3,%,,0,0,0,2,10,0
n4=,10,+,,0,0,0,2,10,0
n5=,93,,,0,1,0,2,10,0
n6=,13,~,,0,0,0,0,0,0
n7=,8,&,,0,0,0,0,0,0
n8=,4,@,,0,0,0,0,0,0
n9=,9,%,,0,0,0,0,0,0
n10=,11,+,,0,0,0,0,0,0