Sample colour and fill the whole image

set cut_paste_input [stack 0]
version 12.2 v5
push $cut_paste_input
Expression {
expr0 "\[sample this r colourPicker.x colourPicker.y sampleSize sampleSize]"
expr1 "\[sample this g colourPicker.x colourPicker.y sampleSize sampleSize]"
expr2 "\[sample this b colourPicker.x colourPicker.y sampleSize sampleSize]"
expr3 1
name sampleColour
selected true
xpos -155
ypos 588
addUserKnob {20 ColourPicker l "Colour Picker"}
addUserKnob {12 colourPicker}
colourPicker {709 358}
addUserKnob {16 sampleSize}
sampleSize 4
}