Slice top or end off watermelon. Cut a thin slice off opposite end so watermelon can sit flat. Scoop out watermelon in balls until you have 4 cups. Remove remaining watermelon to make a bowl; refrigerate cut-out watermelon for another use. Cover watermelon shell and chill.
In a large bowl, place 4 cups watermelon balls, honeydew and cantaloupe balls, strawberries and grapes; set aside.
In a small bowl, combine honey, paprika, dry mustard and salt. Stir in
vinegar. Slowly whisk in oil until thick and emulsified. Stir in 2 teaspoons of the sesame seeds. Pour about 1/2 cup of the dressing over fruit in large bowl. Stir gently until well coated. Cover and chill at least 1 hour. Set remaining dressing and seeds aside.
To serve, place fruit in watermelon shell. Sprinkle with remaining sesame seeds. Garnish with mint leaves. Pass remaining dressing separately.