Blues guitar chords have a distinct sound. That sound is the Dominant 7 chord (R 3 5 b7). Dominant 7's are Major triads with a flat 7.
Get these shapes in your hands. Once we know these fretted versions, it is the same quality (in this case, dominant 7) everywhere we move it (in every position). When we move the shape to a new position (fret number), the root changes, but the type (quality) stays the same.
We call this mileage. We gain a lot of distance by knowing one thing. Closed chords [no open strings] are always the same quality when moved. We get 12 for 1.
Practice fretting & moving a single voicing type linearly. Then practice playing in a neighborhood, say positions 1 through 3, then practice the 8 to 10th position neighborhood (this means mixing forms). Play the blues progressions.
A tritone is an interval of a diminished 5th (or augmented 4th). It is 6 half steps. 6 half steps are 3 whole steps. 3-steps = tri-tone. Tone is sometimes used in music to mean a whole step (I Love Guitar attempts to avoid this double/triple/quadruple meaning).
The neighboring aspect to the tritones is very interesting. You could play the blues and get the sound with just these intervals. Blues guitar chords typically include this interval (dominants 7ths definitely).
The Roman numerals indicate root movement. To play in a neighborhood, follow the I, IV, and V. We always want to know where the roots are located. Root movement gives directionality to harmonic rhythm. Follow the roots.