It's the ultimate wedding guest gaffe - and even pop royalty isn't immune to making this sartorial mistake.
Former Spice Girl Melanie Chisholm was surrounded by famous friends and family as she married Chris Dingwall last weekend.
While all of her bandmates attended except Victoria Beckham, who was in the US for the World Cup final, it was Geri Halliwell's outfit that sparked debate online.
Fans were quick to point out that Geri, who is known for almost exclusively wearing white, may have chosen the wrong colour for one of her oldest and closest friend's big day.
She arrived in a romantic, flowing white dress - a shade that should be reserved for the bride.
For Amanda Wakeley OBE, the issue is less about tradition and more about consideration.
'Unless the bride has specifically asked for it, white should always be left to her,' the British fashion designer and author, who famously dressed Diana, Princess of Wales, tells the Daily Mail.
She explains: 'It's not about outdated rules; it's about respect. A wedding is one of the few occasions where someone else should quite rightly be the centre of attention.
'White naturally draws the eye because we associate it with purity, ceremony and celebration. Wearing it as a guest can unintentionally compete with the bride, even if that wasn't the intention.'
Award-winning personal stylist Lisa Talbot shares a similar view. 'Even if the dress isn't bridal in style, an all-white outfit can still draw unnecessary comparisons and, in photographs especially, can appear as though you're trying to make a statement,' she says.
Colours to avoid
White isn't the only shade that can raise eyebrows at a wedding.
Both experts advise steering clear of neon colours such as acid green, fluorescent pink and highlighter orange.
As Amanda notes: 'Weddings are about celebrating the couple, not making the loudest fashion statement. There is a difference between confidence and demanding attention.'
Red, meanwhile, remains one of the more divisive choices for wedding guests, according to Lisa.
'There's no etiquette rule that says you can't wear red, but it is an inherently attention-grabbing colour.
'If you're attending a traditional or more formal wedding, it's worth considering whether a bright pillar-box red dress could inadvertently draw focus away from the couple.'
For those who love the colour, softer berry tones, burgundy or deep wine shades can offer a more understated alternative while still feeling elegant.
As with any wedding outfit, context matters - the venue, dress code and style of celebration should all inform your choice.
What to wear instead
Rather than focusing solely on what to avoid, Amanda believes wedding guests should choose colours that suit them and inspire confidence.
'The best colours to wear are the ones that you are instinctively drawn to and enjoy wearing and that are flattering to your colouring.
'If in doubt about the colour you are considering take a selfie in the mirror and reflect on how it looks on you… it is often easier to be objective this way.'
Lisa recommends soft, romantic shades that feel celebratory without dominating the occasion.
'The safest and most sophisticated choices tend to be soft pastels, powder blue, sage green, blush pink, lavender, butter yellow or elegant floral prints.
'These shades feel celebratory, photograph beautifully and allow you to look polished without overshadowing the bride. Rich jewel tones such as emerald, navy or plum also work beautifully for autumn and winter weddings.'
If in doubt, look to the Princess of Wales
When it comes to wedding guest dressing, Lisa points to the Princess of Wales as a masterclass in getting it right.
Catherine consistently opts for elegant silhouettes and refined colours that complement the occasion rather than compete with it - most recently demonstrated at the wedding of Peter Phillips and Harriet Sperling.
Lisa praises the Princess' impeccably tailored ensembles and thoughtful accessorising, which strike a balance between sophistication and respect for the event.
As she puts it: 'She demonstrates that you don't need to wear the boldest colour in the room to make an impact.'
Amanda agrees, highlighting Catherine's ability to communicate respect through her wardrobe choices.
'The Princess of Wales understands one of the most important principles of style: dressing for the occasion rather than for herself.
'She always looks polished, but she never overshadows the event or the people at the heart of it. That balance is surprisingly difficult to achieve.'
The bottom line
Ultimately, wedding guest dressing is less about rigid etiquette and more about understanding the occasion.
The venue, dress code, season and, above all, the couple themselves should guide your choices. When in doubt, elegance will almost always outshine extravagance.
As Lisa says: 'The best wedding guest outfit is one that makes you feel confident while allowing the newlyweds to remain the stars of the day.'
Amanda echoes that sentiment, drawing on a theme explored in her latest book.
'In my new book Style DNA: How To Dress With Confidence, I write about clothing as a form of communication. Every outfit sends a message before we've said a word. At a wedding, the message should be: "I'm here to celebrate you."
'The irony is that when you stop trying to be the centre of attention and instead dress with thoughtfulness, confidence and authenticity, people often remember you and your style far more positively.
'True elegance is never about competing for the spotlight; it's about understanding exactly when to let someone else shine.'
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