GIMP Script-fu

sg-select-similar-colors
Login
Command:
Similar colors
Menu:
"<Image>/Select/Similar colors"
PDB Name:
script-fu-sg-select-similar-colors
Download:
sg-select-similar-colors.scm (after the page appears, click on the "Download" command)
License:
GPLv2+

Description:

This script mirrors the functionality of Select By Color Tool, but permits specification of the color (rather than picking it from the image). Other than the Color specification swatch, all options in the dialog correspond directly to those of the Select By Color tool's Options.