How to change it ? All of my texts look very sad 
.
You need to add a new material - go to Assets > Create > Material. In the Inspector panel, you will see the material with options for changing its colour and other properties. Drag your new material onto the materials list of your object (to replace the “Default-Diffuse” which is already there). Whenever you change the colour of the material asset, all objects which use that material will change colour too.