Quartz Composer has a hidden setting. Holding the option key while selecting Preferences from the menu. In the (Editor) pane, there will be an 'uncorrectedCoreImage' setting. Check it on, close QC, then re-open it. Now all filters will run in an uncorrected color space. Repeat the procedure to go back to normal color space conversion.
Other than this, I don't know of any way to change color spaces within Quartz Composer.