FRLG outfit. Probably my favorite of them all.

T5J8F8 said:
FRLG outfit. Probably my favorite of them all.

She is wearing a yellow belt, a black collar and her boots are partly yellow, without any yellow socks.

These may be negligible details, but they mean that, strictly speaking, this is one RGBY outfit, as noted by the image text.

Bulbapedia has an image of that costume with the text "Official artwork from Generation I." It seems it was later adapted, just a little, into the FRLG outfit.

NeverGonnaGive said:

FRLG outfit. Probably my favorite of them all.

This is the red and blue art. In FR & LG, she doesn’t have a belt and in yellow there isn’t any black on stomach area just yellow.