Hi Seymour,
As I am a newcomer to Inkscape and to Gimp, can you tell me how I can obtain black and white on an image by just knowing the numbers #ffffff00 to #00000000; or any other color? How can one bring in a color by knowing the number..
I'm not sure if there's a way to feed Inkscape the opacity in the first suggestion I post here, maybe someone else can enlighten us?
Without transparency:
Have the desired hex value, say #bb0000 in the clipboard, select the object in Inkscape that you want to colorise and then right-click on the fill rectangle on the status bar (it's in the bottom-left corner of the Inkscape window and has the character "S" in front of it). You'll get a context menu in which you can paste the hex value (color) you copied to the clipboard.
With transparency:
Select the object you want to colorise, then hit CTRL-SHIT-X to open the XML editor, find the object and edit the "style" attribute. There's two entries called "fill" and "fill-opacity".
Hope that helps