IFX-Supreme is a cool app, working in much the same way as Graphedit does for media files -- you assemble a chain [graph] of filters that are then used in order. You can also save a sequence of images, showing the progression from un-altered original to onee with the filters applied. As graylox posted, this isn't your typical, add canned FX app.
As far as registration/activation goes, I unchecked Wordwrap in Notepad while viewing the GOTD readme.txt file, double-clicked the key to select, then did a normal copy/paste -- worked fine... The menu item to add the key went away after re-starting the app, but the About box reflected registration immediately.
As far as the dark GUI goes, there's a ui.xml file -- edit the RGB values to suit you, after saving a copy of the original of course.
That said, most monitors aren't calibrated, & I think it's very likely most people haven't tried to adjust their monitors, relying on whatever included presets instead. Typical LCD monitors cannot display the full range &/or gamut of colors, & those presets try to make up for such shortcomings. It's Very common for the black end of the spectrum to be crushed, i.e. there's little visible difference, if any, between black & the darker grays, which could [likely would] make the IFX-Supreme program window almost unusable. IPS monitors OTOH tend to show a much broader, complete spectrum of colors -- many are calibrated right out of the box, and can be re-calibrated as necessary, but they're a lot more expensive, e.g. Apple's Cinema displays [ http://www.apple.com/displays/ ]. Fortunately there's a new type of IPS display that's becoming more common, & in fact the same basic panel's been on sale recently from over 1/2 dozen manufacturers, varying in price from ~$140-$160 for a 23" class monitor. It is not like the full IPS panels, cannot display as wide a gamut, cannot display every color, & doesn't have the full calibration settings, but it does give you a [IMHO much] larger range of colors to work with than a traditional LCD monitor. I'm using one right now & don't have any difficulty using IFX-Supreme.