I think you are referring to the chemical in their exoskeleton that glows when exposed to a 'black" light (like for posters). This also happens to a lesser degree when they are exposed to fluorescent lighting too which can give them a greenish tint.
Although the exact shade of blue/green varies from species to species, as Phil says they all glow.
Any light source with high UV will cause this, be it a UVB tube ("black light"), a full-spectrum reptile bulb, or the sun...it just appears brightest under the black light because of the abssence of visible ("white") light.
Scorpions will also vary to a great degree when highlighted with full UV rays in a similar form to blacklight. Special bulbs can be purchased which are unlike blacklight (only being near UV, while the UV bulbs are full UV) and like blacklights in that they have very little visible light which escapes. These are rarely used (because their cost and adverse effects they can cause over extended use) to create a blue glow on emps and other normally green glowing scorpions and an almost white glow on scorpions that under a blacklight, would usually glow yellow-ish (for instance, Deathstalkers). O. glabifrons can be made to glow more extreme blue colorations as well and often a white-ish color.
Actually guys, there are a few species that do not fluoresce under a UV producing light source...though you will never see any of these in the hobby as from what I understand are quite rare and at least one of them is only found in Mexico. Also, freshly molted scorps won't fluoresce until their new exoskeleton begins to harden...first instars ususally do not fluoresce either.
This may have something to do with the minerals in the new exoskeleton that have not fully crystalized. The different shades of the flourescence have to do with the original color of the exoskeleton making it appear different colors. You have a yellow scorp and the fluorescence will lean a bit more toward the green...a black scorp and it generally moves to a more bluish color. Also, any ambient non-UV light will have an effect. I have observed, and I am sure most of you have, the brightness of the UV source also affects the coloration...i.e. The coloration gets 'whiter' as the UV intensity increases.
If you would like a technical description of how the fluorescence occurrs PM me and I can explain the physics of it.
There is the potential for it to damage their eyes by fogging the clear portion of the exoskeleton...or so I have been told. Also, constantly keeping a Scorp under a BL will diminish the ability to fluoresce. Depending on the type of UV source used there is the possibility that too strong a source might hurt or even kill them...thats one reason you should never put their enclosure in a constantly sunny area.
Ok, I found the e-mail where someone mentioned the species that do not fluoresce but it is a paper copy and I don't have it with me at work so this is to bump it up so I can find it easier when I get home...there were three species that were mentioned off the top of the persons head in the e-mail...I don't remember what they are at the moment but I will try to post them this evening sometime.