[Markovnikov]

I recently performed an ozonolysis in chem lab, but I was wondering a couple of things regarding it.

The temperature set was -78 degrees celsius. Is this low temperature required for the ozone? Or is it due to the unstable intermediate formed?

Also, the addition of ozone was stopped when the solution turned blue. Where does the blue colour come from? 

Thank you for your time.

[Borek]

What is color of ozone itself?

[Markovnikov]

I never got a chance to see it, as it was bubbled through the solution.

But since you're suggesting it, perhaps ozone is blue?

[orgopete]

An ozonolysis reaction does not necessarily require -78°C. It may be wise for your example however, but I don't know. 

[Ulfsaar]

In another chemical bbs, someone said the tempreature should be controled -30C to avoid of other side reactions,but -78C is too low to make such a reaction..
 and the pure ozonide is the  color between the blue and black ,but in solution (like DCM) the color is deep  blue

[baboom]

Hi there,
The low temperature is set to allow ozonolysis to take place, otherwise, the reaction intermediates would be too unstable to form, and the reaction would not take place. In addition, this low temperature is set to allow the gas dissolve in the solution (gasses dissolve better in low temperature). You stop the bubbling of ozone once the solution turns blue, because at that point the solution is saturated with ozone. 

Ozone is not colourless, but blue, because of the movement of electrons through the molecule (the double bond is shifting positions constantly).

[baboom]

Sorry,
I answered the question incorrectly:
Here is the right answer (from wikipedia):
Alkenes can be oxidized with ozone to form alcohols, aldehydes or ketones, or carboxylic acids. In a typical procedure, ozone is bubbled through a solution of the alkene in dichloromethane at –78 °C until the solution takes on a characteristic blue color. This indicates consumption of the olefin