My thoughts on the topic are that there was no reason to change from the traditional colors to begin with and it causes a viewing and playing confusion that is highly detrimental to the game and highly detrimental to the viewing experience. And even if the changes were halfway justifiable at one time (and everybody knows the real main reason for the changes was actually branding), with today's color accurate and highly detailed phone and tv screens it is no longer needed so whatever flimsy excuse you had at one time is now gone.
That said, I think most people could grudgingly accept changing the colors on a couple of balls such as changing the seven ball from red to brown. They don't like it, and they think it is dumb, but they can grudgingly learn the new color and learn to live with it even if they don't like it and don't want it. Because there has never been another brown ball in pool before, you can train yourself to learn that when you see brown it is the seven ball. But for hundreds of years the four ball and only the four ball has been purple and only purple. Purple IS the four ball, period, and there is no training yourself around that and people will forever be making mistakes and getting themselves confused since the four and only the four has been purple and only purple for hundreds of years and so moving a traditional color from one ball to another will never be acceptable. You can replace ball colors (changing 7 from red to brown), but you can never move a traditional color from one ball to another (moving purple from the 4 to the 5).
Sorry Matchroom but your "but we already made the four ball pink" excuse is not a good enough reason to move the color purple over to the five ball. Your pink ball has twenty years of niche history on .01% of ball sets. The color purple has hundreds of years of history on 100% of ball sets and even today is still on 99.99% of ball sets. If a ball color has to be moved then move the pink that has very little history over to be the five ball (or better yet just get rid of pink and make the five ball orange again) because it is more respectful of hundreds of years of history and because it will be the choice that causes faaaaaaaaaaaaar less confusion for everybody.
To move the color purple to a different numbered ball so you don't have to move the pink to a different numbered ball is the absolute height of arrogance (and shortsightedness) on Matchroom's part. By doing so they are essentially saying they believe their couple of years of exceptionally niche ball color "history" is more important than hundreds of years of universal pool ball color history, but even more than that they are showing a total and utter disregard for the viewing (and playing) ease and pleasure of all fans everywhere. Because of their extreme arrogance and bad decision making in this regard I intend to limit my viewing of Matchroom events as much as possible until it is rectified. We can live with replacing a color (such as changing the seven from red to brown) if we must, but what we cannot live with under any circumstance and nor is there any good reason for is moving a universally known historical and traditional color such as purple from one ball to another like from the four ball to the five ball. If you are using a historical and traditional color, it can only be used on the historical and traditional number it has always been used on and cannot suddenly and confusingly be moved to some other ball number after hundreds of years.