Vielen Dank, funktioniert bestens
Hab's so umgebaut:
Delphi-Quellcode:
procedure MarkLineNo(LineIndex : integer; clColor : TColor; Start, Length: integer);
begin
with form1.RichEdit1 do begin
SelStart := Perform(EM_LINEINDEX, LineIndex, 0) + Start;
SelLength := Length;
SelAttributes.Color := clColor;
end;
end;