You should buy the Kendo clothing (Gi, Hakama) after a series of training sessions, when you are certain that you want to continue to practice kendo. This may occur after a few weeks or a few months.
The Gi and Hakama developed from the clothing of the Samurai. The coarse material of the Gi ought to both cushion impact and absorb sweat. With its air cushioning, the Hakama also serves to minimize the impact of your opponents blows, and, with its fastening bands under the belly button and its trapezoid-form back piece, it supports the mid-body posture, which is essential in kendo.
The Gi and Hakama should be made of blue cotton. Black is not typical in kendo. White is also rare, and when worn, then typically by women. For transport you should always fold your clothing neatly together so that the clothing retains its form and the form of Kendoka helps.
The color of new clothes bleeds during washing and training for a long time. This is not a sign of poor quality.