Hi,

- please open the attached spreadsheet (cell A4 should be selected)

- press F2 on cell A4 to edit it's formula:

Note the colored cell references and the colored cell borders.

- Now we want add the content of the cell A3 to the formula, so enter "+A3":

Note that the colors have vanished, after you have started typing.

Oder spreadsheet software like Excel and KSpread set the colors "on the fly"
while editing formulas. Calc should the same.

(Even if only the arrow keys are used to move the cursor through formulas, the
colors are vanishing, although the formula has not been edited.)