Does light glow white when its,t reach the ultraviolet ?

White is visible light spectrum combined... ultraviolet is above the visible spectrum. What are you asking?

Like vapor mercury gas that produce with glow white light with ulravoilt light

Most mercury gas lamps produce a bluish glow, if not an aqua color. Depending on the internal pressure of the lamp, it can be almost all UV and will appear bright lite blue.

If they are being used for lighting only applications they usually put a phosphorus coating on the glass. This converts some of the UV to Red, making the light look more white and less blue.

I now the atom has each level energy for different color . But how does the color mix together to produse white light

Yeah, the vapor mercury produces high amounts, when it hits the phosphorus a good majority of it is "modulated" to visible red which when mixed with lower end of the light being produced by the mercury vapor (would be blue-purple) it balances the light spectrum. This gives it more of a white appearance as opposed to the blue you would see and the UV you wouldn't see.

When all light colors are mixed together (ROYGVIV) you get what appears as pure white light. You can send pure white light through a prism to separate it back into the entire rainbow. The modulation just balances it so it appears more white.

Does ultravoilt is a white lihgt

Ultraviolet is NOT white light.

White light is a mixture of several different electromagnetic waves found within the visible spectrum of light.

UV has a greater frequency, or shorter wavelength and cannot be seen by our eyes.

Now I know uv is not white light but how the colors mix togther out side from the atom . Like all the colors meet togther in one point and produce white light

I think it's due to interference. The electrons in atoms change orbitals, creating an electromagnetic wave. Since there are many electrons changing different energy levels, you get different wavelengths of electromagnetic wave. When these waves meet, interference occurs, altering the amplitude and wavelength of the resultant electromagnetic wave.

The atoms are not responsible for light. The energy they produce is in the form of light. So, once the energy is released, you don't need atoms any more for light to be there.

Does that answer your question? :)