Prince Harry has been advised not to propose to Meghan Markle with an emerald ring.
The couple have only been dating just over a year, but rumours about when they will take their relationship to the next level have been rife since the beginning of 2017.
And, although royal fans have been speculating that the 33-year-old prince will incorporate a piece of his late mother Princess Diana's jewellery into the engagement ring, jewellery specialists have warned him to be selective about the stone he uses.
Tobias Kormind, founder of 77Diamonds, told the Express.co.uk: "Engagement rings are our core product. We are working on a concept where we will launch coloured stones.
"It's interesting because at the high end these are performing really well - the sapphires and emeralds - because they are quite rare, and they are absolutely beautiful, and we all love colour. But I think its much better if you do earrings or pendants with those stones rather than the knuckle duster ring!
"Gemstones are softer, so over the course of a lifetime they won't last, so unless its a ruby or a sapphire we do say, especially for engagement rings, that they are prone to chipping and breaking. Unless the stone was too soft to set we would never say no to creating it, but we would definitely advise against every day wear."
But the flame-haired prince doesn't have to stick to a white diamond as he could opt for a coloured one - a rising trend in today's society - when he pops the question.
Mr Kormind explained: "Tiffany bought into a mine that produces a lot of yellows, so they made yellow diamonds a really big thing, and there was definitely a trend for yellow but I think that's dissipated a little bit.
"There have been some amazing headline auctions where records have been broken on the blues and the pinks, but the problem is they are out of reach for most.
"A decent sized blue or pink costs hundreds of thousands of pounds. A one carat white diamond of decent quality would cost a few thousand - the equivalent blue would be about half a million pounds, a pink would be about £300,000.
"But if you think about the chemical probability of achieving a decent quality blue or pink diamond, it is very rare, so completely worth the money it is achieving at auction. You look at these stones and they like rare masterpieces; you can compare them to art."