If you don't know what guitar scales and mods are, please take a look at the Guitar scales wiki page first and then come back for some colorful fretboard visualization.
FretViz is designed around the idea of color synesthesia which exists in two different forms. The first one is called projective synesthesia which means that there are people who see actual colors when they hear a note or a sound. The second one is called associative synesthesia which can be trained in a similar way as the brain can be trained to memorize vast amounts of pi decimals for example.
This is where FretViz comes in! You can learn to memorize the fretboard and scales by associating colors with the notes on the fretboard. Clicking a note on the fretboard will play the corresponding frequency with a flash of the note color to make the association stronger.
Each note can be assigned a color from the right side color selects. By default every note has a different color which makes it easy to find single notes and patterns on the fretboard. Feel free to experiment with the colors and try to assign notes with colors that feel like the sound it makes. Each note can also be deactivated to remove it from the current visualization.
One of the main features in FretViz is the scale generator though you can also easily make your own scales by deactivating specific notes or you can load a pre-made scale and modify it to your liking. Start using the scale visualization by clicking the upper right scales button.
The tuning and the octaves can be changed from the dropdown selects on the left side of the fretboard. The standard guitar tuning is of course EADGBE which is also the default tuning in FretViz. For more information on different guitar tunings you can visit the Guitar tunings wiki page.
Normal guitar has six strings but this is not always the case. For example the bass guitar usually has only four strings. The and buttons can be used to add or remove strings from the fretboard configuration to match your current instrument or you can also select one of the preset instruments.
By default FretViz is showing 18 frets which covers most of the fretboard but you can also display 12 or 24 frets if you like. There are 12 frets in a full octave as you probably know already.