Could sign colours (motorway, primary route, local route, roadworks) be standardised?

Anyone who has driven through Europe will have noticed that the road sign colours are not uniform for motorways, primary routes, non-primary / local routes, and roadworks signs. The differences are explained in more detail here. Could the colours for these signs be standardised in Europe, if not worldwide? Even though there is no safety issue from leaving things as they are, the purpose of this article is to start a discussion.

As demonstrated in the link above, many countries in Europe use blue for motorway colours (UK, France, Germany, Ireland, Netherlands, Spain, etc.), there are also many who use green (Italy, Switzerland, and Sweden for example). For primary routes, the UK, France, and Ireland all uses green, whereas Germany and Luxembourg uses yellow (the colour of roadworks in UK and France), Sweden uses blue, and Spain uses white. For local routes in the UK, Ireland, and France the colour is white, whereas white is used for urban routes only in Germany. So this alone illustrates that there is no uniformity regarding colour schemes in Europe, let alone the world.

I believe there is no serious safety issue from leaving things as they are. Someone from the UK might mistake a primary route for a motorway in Sweden on signs where no motorway symbols are present, and vice versa, but that's about it - but this can easily be rectified by being familiar with signs before visiting anywhere. But standardisation does make life much more convenient, because this then means you only need to learn one set of signs in your home country, and it would be the same everywhere.

I think that if this was ever to be proposed, I would naturally suggest using the UK colour scheme of blue for motorway, green for primary routes, and white for local routes. However, I would suggest black text on a yellow background for temporary signs instead of the white text on a red background currently used in the UK (Black text on yellow background is easier on the eye than white text on red).

Although this is not an important issue, I was wondering what you think. Should we standardise on a single colour scheme for motorways, primary routes, local routes, and roadwork sign colours, and if so, what colours do you think should be used within Europe (and internationally)? Please feel free to discuss.