Wet blending with oil paints is much easier than working with acrylics. Oil paints take days to dry, which leaves plenty of time to manipulate the paint to the result you desire.
For power weapons, I use a series of three colors from Winsor & Newton Artist's Oils: Prussian Blue, Ultramarine Green Shade, and Titanium White.
You will also need a small (0 will do fine) synthetic brush. I have had better results with synthetics than natural hair when it comes to oils (acrylics are a different story). You'll need paper towels too.
Undercoat in the medium range of your desired colors (in this case, a mid/dark blue). Oils, especially some of the lighter colors, become transparent as they are thinned. This makes undercoating a necessity.
Once you have your three colors on your palette, decide which way you want the highlights to go. Using your brush, apply each of the colors equidistant along the weapon, cleaning the brush on the towel between each color application. Apply the colors in a lightest to darkest/darkest to lightest fashion. As the blade below has two angles on each side, I kept my colors restricted to one side of the blade. I'll blend in the opposite direction for the other side to get a more noticeable affect.
Once the paint has completely dried (several days). Apply a matte coat to protect your hard work!
Here are a few examples of other power weapons done in the same way.