One major reason for the change (in addition to making refereeing easier) was to make judo more appealing to TV audiences, and in this the IJF explicitly disavows any responsibility to adhere to Japanese aesthetic or traditional values (and hence no pressure to consider e.g. indigo):
As the birthplace of judo is Japan, the techniques and spirit of judo are qualities which we should strive to develop as members of the judo community, however it is not the responsibility of the judo community to spread the Japanese culture through promotion of its traditions.
- Introduction of the Blue Judogi, the New Tradition
Early reports of the blue judogi's use pre-adoption by the IJF make note of it specifically being chosen for its 'dazzling' effect on TV, and hence would explain why a bright blue was chosen:
Television turns judo blue
From next January 1, the judo competitions at European level will be held with one competitor wearing the standard uniform and his opponent wearing a striking blue jacket and trousers which should dazzle television viewers. One thing will remain the same for both fighters, however - the traditional black belt.
Judo traditionalists singing the blues
In certain respects1, it is like the process of liberalization of agricultural imports. Pressured by judo circles in Europe, Japan will likely have no choice but to approve the use of color uniforms in the ancient sport.
One competitor would wear a traditional white uniform, as in the past, while the opponent would don a blue outfit2. With such a color distinction, it would be easier for the referee to make decisions and also help the audience understand the match. Besides3, color uniforms look better on TV. Citing such reasons, Anton Geesink of Holland, who won a gold medal in the open4 weight division in the Tokyo Olympic Games, and others have promoted color uniforms.
As for [the Japanese argument5 against the trend that the white uniform is the symbol of a pure heart and should be preserved as a tradition], Geesink has said that the Japanese are free to be sticklers for white and stick to tradition, but that it will not pass muster6 in the international arena.
As for why blue itself was chosen, as opposed to e.g. red (as in the red/blue uniforms in taekwondo, wrestling, boxing etc), Geesink himself did consider red judogis early on:
Though I presume they were ultimately discarded in favour of blue to ensure any cuts were quickly noticed, since blood would not show as clearly on a red uniform (as indeed is the rationale of the JBBA).
The following report makes the curious claim that the contrasting colours have greater symbolic implications, though I'm not certain what the explicit meaning is:
Although it used to be the tradition for practitioners of judo to wear a “judogi” that consisted of a loose-fitting jacket and trousers in white cotton, the International Judo Federation (IJF) decided at a general session held in 1997 to introduce blue cotton judogi as a sign of the international status of the sport.