4.6 Four table tennis players are dressed in 4 different colors for a performance match, with 2 in red, 2 in yellow, 1 in blue, and 1 in black. Each performance selects 3 players to appear, and matches are only played between players with different colored outfits, with the specific rules being:
(1) If the "3-person group" on stage has all different colored outfits, then each pair of players will play 1 match, and players who have already played against each other in different "3-person groups" will still play again if they meet;
(2) If the "3-person group" on stage has 2 players with the same colored outfit, then these 2 players will not play against each other, and only 1 of them will play 1 match against the other player.

According to these rules, when all different "3-person groups" have appeared, a total of $\qquad$ matches have been played.
4.44.

Represent the 2 athletes in red as two parallel lines $l_{1}$, $l_{2}$; the 2 athletes in yellow as two other parallel lines $l_{3}$, $l_{4}$; and the athletes in blue and black as intersecting lines $l_{5}$, $l_{6}$, which intersect with $l_{1}$, $l_{2}$, $l_{3}$, $l_{4}$. This results in Figure 6, where there are no "three lines intersecting at a single point".
(1) When the "group of 3" have different colored outfits, according to the rules, this corresponds to three lines intersecting pairwise, and the number of matches is exactly the number of line segments in the figure (Figure 7).
(2) When the "group of 3" has 2 athletes with the same colored outfits, according to the rules, this corresponds to "two parallel lines being intersected by a third line", and the number of matches is exactly the number of line segments in the figure (Figure 8).
Thus, we only need to count the number of line segments in the figure.
First, $l_{1}$, $l_{2}$, $l_{3}$, $l_{4}$ each have 4 intersection points, and each line has 6 line segments, totaling $6 \times 4 = 24$ line segments, corresponding to 24 matches.

Second, $l_{5}$, $l_{6}$ each have 5 intersection points, and each line has 10 line segments, totaling $10 \times 2 = 20$ line segments, corresponding to 20 matches.
Adding the two cases together, the total number of matches is $24 + 20 = 44$.