GIMP :: Changing Colors With Colorize?

Somebody want me to edit their picture where an orange tank top has to be changed for a dark blue color. That person did provide the specific HTML code # for the color wanted. Once the tank top is selected, how do you manage to colorize it to that very specific HTML color. Unless I'm wrong, "colorize" is the only function that add color to something without losing the detail of the original picture. All other thing you can use to change the color only add a solid opaque color. You can desaturate the tank top,open a new layer and add the specific HTML color to that layer and then reduce the opacity but...even thought the details that were lost are now visible, the color has changed.