It is a yellow rubber ball with a red stripe around it and a blue star on 1 of the yellow sides. In some episodes, some colors are reversed (the ball is red and the stripe is yellow) or are different colors altogether. Any of these balls can be animated or even live action (which Steve or Joe can interact with).
It appeared at the beginning of every episode from the 1st to the 3rd seasons and most of the one for the 4th season except for "The Anything Box", "Adventure", "What's New, Blue?", "Bugs!", "¡Un Día Con Plum!", "Blue's Backyard Ballgame Bonanza", "Let's Plant", "Joe Gets a Clue", and ; and at the end of the end credits of all episodes except for "Blue's Big Musical", "Blue's Big Pajama Party", and "100th Episode Celebration"; as well as in many other episodes.
The ball's 1st official appearance in an episode was the 2nd one: "What Time Is It for Blue?". It was the last toy to put away.
In "Blue Goes to the Beach", a red ball with an orange stripe and a green star appeared near the pool at the end.
A red ball with an cornflower blue stripe and a blue star appeared on the middle section of the shelf (slightly behind a red baseball bat and to the left of a white baseball with red lacing) that the 1st clue (a horn) was on top of in "The Trying Game". The ball that the pigs were playing with looked just like it, only the stripe was yellow and the star was medium blue.
In "Blue Wants to Play a Game", the ball was seen in the toy box in front of and between a white roller skate with powder blue wheels and lacing and a black bumper and a red wooden letter Q block and behind the left side of a white jumprope with gray-blue handles. Blue hid behind the toy box when she and Steve played hide and seek. A deep sky blue version of the ball with a bright navy blue stripe and a vivid blue star was also among the blue objects that Blue hid among and Tickety Tock had the ball as the symbol for 12 during that time (The ball's outline, stripe, and star outline were all medium purple).
In "Hide and Seek", the object that Cybil Circle was looking for was a gold felt version of the ball with a red stripe and star, which she gave to Steve (becoming a real ball when she did). The ball was later used at the end of the episode to find Blue under the bed.
In "Blue's Big Treasure Hunt", a sparkling version of Blue's ball appeared near the pot of chocolate coins at the end of the rainbow in the Land of Great Discovery next to a sparkling version of Steve's bunny slippers.
The ball also made several appearances in about all Blue's Clues video games
The ball appeared in "Blue's Birthday Adventure", "Blue's ABC Time Activities", "Blue's 123 Time Activities", "Blue's Treasure Hunt", "Blue's Reading Time Activities", "Blue's Art Time Activities", and "".
In "Blue's Birthday Adventure", the ball appears to the left of the toy chest located in the right side of the living room with the skidoo picture frame in all 4 scenarios in addition to their opening sequences (just like in the episodes). Sometimes, when Blue enters that room, she will bounce the ball with her nose to where the picture frame is located and in front of the rubber duck, then use her right ear to toss it back to its original place.
The ball appeared several times in "Blue's Alphabet Book". It also represented the letter "B" in the book.