Whatdotcolor
From Compsci.ca Wiki
Also spelled whatdotcolour (Canadian spelling of colour), it is a Turing function which returns the colour of a specific pixel. Often used for collision detection, it is an easy solution when creating something using Turing graphics alone without external images being involved.
It's actually so important that there's a whatdotcolor Warrior mod.
Here's a quick example of a few basic graphics functions which uses whatdotcolour to check if the mouse is above a red circle.
%%Example of whatdotcolour collision detection
%%By: Gandalf
setscreen ("graphics,offscreenonly")
var cx, cy, mx, my, mb : int
cx := maxx div 2
cy := maxy div 2
var circleColour : int := red
loop
cls
Draw.FillOval (cx, cy, 40, 40, circleColour)
Mouse.Where (mx, my, mb)
%if your mouse is above the circle and you click
if whatdotcolour (mx, my) = circleColour and mb > 0 then
%move the circle to the mouse coordinates
cx := mx
cy := my
end if
View.Update
end loop
An alternative of whatdotcolour collision detection in Turing is using Math.Distance.