c1 = nil, while not accounted for in the posted code will not throw any *error* as no Layer Object has a Color Property = nil. However, beware of c2 = nil, as this will cause the code to throw an *error*: [code] ; error: ActiveX Server returned an error: Parameter not optional [/code] Perhaps a better alternative is to use an IF statement to verify the valid input of the color to be replaced and the replacement color. The following code also adds the color dialog for graphical selection, and an undo mark which the code above lacks: [code] (vl-load-com) (defun c:LAYCOL () (c:LayerColor)) (defun c:LayerColor (/ *error*) (vl-load-com) (princ " LAYERCOLOR ") (defun *error* (msg) (if acDoc (vla-endundomark acDoc) ) (cond ((not msg)) ; Normal exit ((member msg '("Function cancelled" "quit / exit abort"))) ; <esc> or (quit) ((princ (strcat " ** Error: " msg " ** "))) ) ; Fatal error, display it (princ) ) ((lambda (acDoc / oldColor newColor) (vla-startundomark acDoc) (if (= "BYLAYER" (setq color (getvar 'cecolor))) (setq color 1) (setq color (atoi color)) ) (if (and (princ " Select color to be replaced: ") (setq oldColor (acad_colordlg color nil)) (princ " Select replacement color: ") (setq newColor (acad_colordlg oldColor nil)) ) (progn (vlax-for oLayer (vla-get-layers acDoc) (if (= oldColor (vla-get-color oLayer)) (vla-put-color oLayer newColor) ) ) (*error* nil) ) (*error* "Color not specified") ) ) (vla-get-activedocument (vlax-get-acad-object)) ) ) (princ) [/code]