The first martial arts tournament that Goku participated was when he launched the outfit he wore in most of the history of Dragon Ball. The design of this iconic outfit has orange shirt with blue bra, blue belt, orange pants and mixed with blue boots.
For many years, it is thought that the orange in Goku's outfit (and Krillin and Yamcha) is an error in the Dragon Ball anime.
Those who claim this, although wrong, have a solid argument to protect their claims. It is said that there are two colors: red for television and orange for manga.
However, after many years, we realized that the drama has turned orange and the first episodes are actually the color tone of the screen in the late 80s and early 90s. Significantly shades and intensity of color, depending on the change in television image quality.
The truth is that Goku's outfit and the tortoise school are orange, and according to Akira Toriyama, there is a reason for that.

Orange goku's clothes in Dragon Ball
According to what Akira Toriyama revealed in an old interview, Goku's outfit was orange because it was inspired by the uniform of the Shaolin monks, traditional people who often wear this color.
Orange is a multi -facetable pigment, which has different meanings in separate cultures. This color is quite prominent in Asian religions, many monks and saints wearing orange cloak.
As is known, author Akira Toriyama has been inspired by Chinese martial arts and culture to design the Dragon Ball series.

In the culture of Japanese and Chinese, orange symbolizes courage, determination, happiness, love and good health. The elements are completely suitable for Goku's personality and the principles of Master Roshi in martial arts.
In short, the iconic orange outfit of strength, determination and spirit of Goku.