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.

   %%Created By: Gandalf
   %%Example of whatdotcolour collision detection
   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 whatdotcolour (mx, my) = circleColour and mb > 0 then
           cx := mx 
           cy := my
       end if
       View.Update
   end loop

An alternative of whatdotcolour collision detection in Turing is using Math.Distance.