At request I've done a power sword tutorial, which is my own take on the space hulk 'blue lightning' effect. It's easier to do than you might think so give it a go. I'll post a 'basic' drybrush power sword effect on here when I get time. Please note: The green was a test for this technique - you can say if it was successful or not!) So here goes...
Step 1: Find out the range of blues (or greens, or reds) that you have and put them in shade order. Some of these I used as extra steps, which you can skip for a quicker effect -I will mark the main steps with a 'KEY' as we go. I missed out camo green on the green stages, because it was clearly the wrong sequence of colours!
After undercoating black - personal preference - never tried this on a white/grey undercoat - try it tell me if it works!
KEY Step 2: Basecoat with necron abyss (blue)
or orkshide shade (green)
KEY Step 3: With a detail brush draw on fairly broad lightning crackles in regal blue
or dark angels green
Step 4: Go over these with a thiner line of Mordian Blue
or Knarloc Green
KEY Step 5: Use an even thinner line of enchanted blue
or snot green
(don't worry if you cover over parts or run onto the base coat (if it's too precise it will look rubbish anyway)
Step 6: Same as above, but using Hawk turquoise
and Scorpion green
(you can begin to use this stage as the start of highlights on key parts of the 'lightning')
KEY Step 7: On parts of the lightning, use Ice Blue
or Rotting Flesh
as a highlight (you can also use this step and the previous one to line the edge of the blade - I like the overall look this achieves - but you can miss it out)
Step 8: You can use space wolves grey as another level of highlighting on the blue.
KEY Step 9: Skull White as the final highlight - really brings out the lightning feel.
You can use the same colours and gradually drybrush a pretty cool looking power sword (tutorial on this to follow).
Examples of power swords past and present!
'Molten' Sword - using drybrushing techniques
An early effort of a Drybrushed blue thunderhammer
Highlighted green power fist
EDIT: In retrospect, including some yellow tones at the top end of the green sequence would have created a better overall effect (I might try this and post the results.