Option C: Red
Let's analyze the information given in the problem step by step:
     ● Queue Order: A, B, C, D, E, F, G  
     ● Cap Colors: Violet, Indigo, Blue, Green, Yellow, Orange, Red  
     ● Statements:  
       1. D can see green and blue, but not violet.
       2. E can see violet and yellow, but not red.
       3. G can see all colors except orange.
       4. E is wearing an indigo-colored cap.
     Step-by-Step Analysis:
         ○ Since D can see green and blue but not violet, it means that the person wearing the violet cap must be behind D. Therefore, A, B, or C cannot be wearing the violet cap.
         ○ E is wearing an indigo cap, so E cannot be wearing the red cap. Since E can see violet and yellow but not red, the red cap must be worn by someone behind E. Therefore, F or G must be wearing the red cap.
         ○ G can see all colors except orange, which means G is wearing the orange cap.
         ○ Since G is wearing the orange cap, F must be wearing the red cap because E cannot see the red cap.
         ○ Now, let's assign the remaining colors:
           ○ A, B, C, and D must be wearing the remaining colors: violet, blue, green, and yellow.
           ○ D can see green and blue, so D cannot be wearing these colors. Therefore, D must be wearing yellow.
           ○ Since D can see green and blue, A and B must be wearing green and blue, respectively.
           ○ C must be wearing the violet cap because D cannot see violet.
     Final Assignment:
         ○ A: Green
         ○ B: Blue
         ○ C: Violet
         ○ D: Yellow
         ○ E: Indigo
         ○ F: Red
         ○ G: Orange
     Therefore, the color of the cap worn by F is red.