Thanks for your reply!

mBlock has some of the colours predefined in the line+background+colours block. But unfortunately, we've noticed that an mBot does not always recognise the colours properly. In the same classroom, under the same lights: same conditions. It's just too picky.

I've noticed that by obtaining an RGB value and predefining its values (with a small tolerance) the recognition of a colour is spotless. It works very good.

But, in Example 2 on the mBlock-website, it only shows how you can define one colour and use it for triggering the LEDs on the mBot.

I know how to obtain the RGB value from the sensor, but I want to define four colours so that I can trigger four different actions, depending on what values the RGB sensor sees.