Change color of icon from black to blue using Gimp

[Redraw]

Hello Sigma
With any object image on alpha you can lock alpha channel as mentioned by Rich 2005,
next I'd grab the paintbrush of choice and colour of choice then paint away

also this option allows for different colours or shades of the one colour,
example top 1/2 light shade and bottom 1/2 darker shades then you could have several loafs all slightly different.
Hope it helps
ReDraw