I think you should see chakra similar to heat. If it is 20 degrees celsius you dont see heat.
Now if its 40 degrees celsius you can see the air vibrating/moving.
First of, people with visual prowesses can see chakra.
Although chakra is usually invisible, those with certain dōjutsu, like the Sharingan, Rinnegan or Byakugan, can see the colour of someone's chakra. Each person's chakra apparently has a different colour.
The second point comes closer to my heat theory
It is also interesting to note the fact that sufficiently immense amounts of chakra are visible to the naked eye.
Here comes the intersting part " When does chakra count as immense ?"
We know that in naruto there is a system simalar to our blood veins, the chakra pathway system. Allong these paths there are special points called Tenketsu.
Though ninja use chakra regularly, very few ninja possess any great control over their tenketsu. Even of jōnin, the vast majority are only capable of releasing a small amount of chakra through their hands or feet to increase the power of punches, jumps, or kicks
The Hyuga clan's main attack focus on closing those Tenketsu. The The Eight Trigrams Sixty-Four Palms closes sixty-four tenketsu.
Though not explicitly stated, it is logical to say that the Hyūga clan (and Neji independently) calculated the exact tenketsu that would be required to shut down an opponent's combat ability.
With this information we can conclude that people whom can still function with 64 tenketsu shut are considerd above normal.
Neji Hyūga was shocked that Naruto Uzumaki was still able to stand after being hit with Eight Trigrams Sixty-Four Palms as his body should have been in a virtually quadriplegic state.
We can also assume that the chakra a bijuu transmits to the user surpases the 64 tenketsu limiter, also the chakra from a bijuu is considerd more pure/powerfull then a normal chakra user
The tailed beasts (尾獣, bijū) are the nine titanic behemoths within the Naruto series. They are living forms of chakra, sometimes referred to as "Chakra Monsters" giving them immense reserves of especially strong chakra that far outmatches most shinobi. The tailed beasts' chakra is coloured red
There are still some mystery's regarding chakra. But as we slowly find out more in the manga/anime a beter answer might pop up.