Several stores are displaying the brand's message: "During Pride, only one rainbow matters. So, we've given up ours to show our support".
The monochrome move is just for the month of June.
The parent company, chewing gum makers Wrigley, said that since both the LGBT community and Skittles share the rainbow as a symbol, "Skittles has again given up its rainbow colours in order for Pride's rainbow to take centre stage".
At last year's London Pride parade the company said they received a positive response to its #onerainbow social media campaign.
Wrigley also said that the monochrome campaign champions "key values for us" like diversity and inclusion.
"This campaign allows us to have great fun with our brand while also raising awareness of an important issue."
At the moment the special Skittles packets are only available at Tesco stores in the United Kingdom.
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