we transferred the microalgae flask to another conditions with more light so the temperature was high?
because we have a problem with temperature in our lab its cold so the growth become very weak but its have a few color....
It would be better to have more information (microalgae species, pigment concentration in the inoculum; light intensity, and so on). But it looks like you stressed you culture. High light itself is a very strong factor affecting growth. If you started experiment with too diluted or weak culture that was not at the logarithmic growth stage, than you created stress conditions by transferring to a high light. Try to start from more dense cultures. It is also very important to have "healthy". You need to make few rounds of growth-dilution series (with constant intervals) before transferring ti high light. Good luck.
What color was your culture originally? The color may have been lost because the increase in light triggered a loss in chlorophyll a. As light increases, the algal cell will decrease the pigment antenna size and the number of reaction centers to avoid capturing light in excess of what it can utilize. We tend to call this process photoaclimation. If too much light is absorbed and the cell is not able to get rid of it through heat dissipation, you may end up "burning" (or bleaching) the photosystems. A good way of sseeing photoaclimation in nature is to look at the green shades in a forest. While the leaves at the top of the trees have light green colors, often with yellowish tones, the shrubs that grow at the shade of the trees will have very dark green colors. This gradient in green reflects the chlorophyll content of the leaves. Those in the top of the trees receive a high amount of light; hence, they do not need much chlorophyll in order to capture the energy needed to grow. The shrubs are exposed to a much lower photon flux (light) and need to ensure they capture every photon available; hence, they carry high amount of chlorophyll per unit cell. The same thing happens with algae exposed to different light conditions.
High temperatura quickly degrade pigments. If temperature is too high your like 'cooking' the culture. Be also sure you have not introduced any bleaching agent. As said above by Nastassia and Ricardo, a proper combination of light intensity and temperatura is necessary to keep the algal cells healthy and growing.
Good luck
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