I am personally very fond of music theory and harmony theory. It’s a never-ending tail of interesting little facts and can-do’s and cannot-do’s. Many of those rules were created in Europe during the Middle Ages when Gregorian Chants were the dominant musical form during congregation. The basis formed what we now call musical modes. Even the very-much known major and minor scales are just ancient modes. In this article I want to take a closer look at modes and how many players use them, but actually don’t know that they use them.
Modes were first described by the English monk and author Alcuinus of York, round the year 800. It’s interesting to note that despite the major and minor scale are just a rework of these ‘church modes’, they weren’t actually accepted by the Church as such. For us to understand how a mode is constructed, let’s take a look at the standard scales we already know, major and minor. For the ease of understanding, I will take the key of C major and A minor as my prime examples, because they don’t need any augmentations to the notes to make their key work.
The key of C major has the following notes. In italic I will give the relative distance of the note to the previous note (with the prime as the exception of course).
C (perfect prime)
D (major second, whole)
E (major third, whole)
F (perfect fourth, half)
G (perfect fifth, whole)
A (major sixth, whole)
B (major seventh, whole)
C (perfect octave, half).
I will do the same for the A minor scale.
A (perfect prime)
B (major second, whole)
C (minor third, half)
D (perfect fourth, whole)
E (perfect fifth, whole)
F (minor sixth, half)
G (minor seventh, whole)
A (perfect octave, whole)
As you can see, both scales share the exact same notes, only the locations of the half steps are different. In a major scale, the half steps are between the third and fourth and between the seventh and the root note. In a minor scale, the half steps are between the second and third and between the sixth and seventh.
You can move around those half steps. By doing so, you get four other modes: Dorian, Phrygian, Lydian and Mixolydian. I will take the scales of C as a means of comparing.

In a Dorian mode, the half steps are located between the second and third and between the sixth and seventh step.

In a Phrygian mode, the half steps are between the prime and second and between the fifth and sixth step.

In a Lydian mode, the half steps are between the fourth and fifth and between the seventh and octave.

In a Mixolydian mode, the half steps are between the third and fourth and between the sixth and seventh step.

Each mode has a voicing, a style of its own. Dorian is a bit serious, Phrygian is just simply sad and almost depressing (a real tear jerker!). Lydian is a bit mystical and enticing, and Mixolydian is a bit in between all of them.
The Dorian mode is also very popular. The Doors used the Dorian mode to write their popular song “Riders on a Storm.” The slight tension you feel when you hear that song is very characteristic for that mode.
On the other hand, Mixolydian is also extremely popular. You can change very easily between major and minor just by changing one note, even within one scale! Joe Bonamassa seems to be a master of swapping between major and minor scales, via the Mixolydian scale. He uses the augmented or diminished (depending on the initial  scale) seven to give his solo a bit more texture. Using the augmented seven in a minor scale (whereas a minor scale only has a diminished third and sixth) will also give you an incredibly nice ‘mood’; something Spanish or Arabic. Just give it a go. It can be some kind of stretch in some applications and sometimes you might even have to skip a string, but in my opinion the benefits outweigh the negative aspects. Don’t linger too long on these ‘off key’ augmented notes since they are just there to add some texture and feel.

Learning the scales can be a  bit daunting because your fingers are very used to playing major and minor scales. But I believe it can benefit your playing greatly. You can add texture and make your solo or riff a bit more interesting.
I realise I skipped on some other modes and didn’t go in detail on how these modes are constructed in terms of temperament. I just want you to get acquainted with some ways to color your solos and riffing in a relatively easy way.