Possible engine damage - Ford ka Trend 1.3?

Please tell me what is the colour of the light that indicates that the engine is overheating? i had an incident last week where my car overheated due to negligence at a garage, the radiator cap was not placed back properly, i did not notice anything while driving on the highway but as soon as i stopped i saw steam came form the bonnet.... could serious damage occurred, i have been driving it since then and no warnings signs are indicated.... a red light appears but as far as i know that indicates low brake fluid.. i do check the water regulary, and there is no oil in the water, and no smoke appears while driving.... could anything be wrong?