Change the colour of an object

The rectangle is a fence, not a mask. Inside it the ordinary selection runs — sampled colour, three tolerances, soft band — so the object's edge is wherever its colour stops, even if the rectangle is generous. Outside it nothing changes, byte for byte.

If the coverage reads zero after you draw, the rail says whether the colour is missing from the picture or simply outside the region, so the fix is obvious: move the shape, or sample again.

1. A background of the same colour inside the rectangle is still selected; tighten the shape or add a “not here” shape over it.
2. A shape belongs to this picture's frame, so it does not carry over when the recipe is sent to the batch queue.

How is this different from replacing a colour?

Replace colour is colour-first: it changes a colour wherever it appears. This door is region-first: you mark the object, and the colour test only runs inside the mark. Use it when the same colour also appears somewhere you want left alone.

Do I have to trace the object exactly?

No. Draw a loose rectangle or ellipse around it, then sample the object's colour. The edge of the change is decided by the colour test, at full resolution on export, not by where the rectangle's edge falls.

Can I type the rectangle instead of dragging it?

Yes. Every shape has four fields — left, top, width and height in per cent of the frame — plus a feather. They are the keyboard and touch route to “only here”, and they are redrawn identically at every size.

• Replace a colourThe dropper armed on open, two swatches, one operation and nothing else to manage.
• The general remapperHue shift, absolute replace and a stack of operations that can be reordered and edited.
• Same colour, two objectsWhy a colour selection cannot tell a blue jacket from a blue sky, and what a region does.

Image data is never posted anywhere: decode, mask, remap and encode all happen inside this tab's memory, and that memory is released when you leave.