McCormik's "Neon Dye" food coloring has good purples and blues, (box with little easter eggs on the front I think) bought mine at Target a few weeks ago.
The purple in there is to die for, you can get extremely concentrated purples and blues as good as the USA made versions if not better. Of course the chart is for food purposes, but I have found that two drops purple, one drop blue, and one drop pink work well for a 52oz. But experiment with a glass of water and hold ever so easilu over the base to see the light passing through it. If the lava is melted and flowing, hold the glass with dyed water up and look through the glass at the lava lamp to test out the color before adding to the lava lamp.
Thanks Coolsox. Have posted a couple of the Blue Fluidium. Still need to switch it to another bottle as some clown on ebay "forgot" to mention half the logo was rubbed off on the bottle.