CLS

Clear the graphics screen and home the text cursor so the next prompt is at the top of HDMI.

CLS [colour]

colour - RGB fill colour (optional). With no argument the screen is filled

with the current background colour (see COLOUR). Use RGB(r,g,b) or
RGB("RED").

Example:

CLS RGB(0, 0, 0)
CLS

Source: docs/help/cls.txt inmmcore. On the computer, typeHELP CLS.