People working in and visiting the town will be invited to dress themselves and their buildings in the colour on Friday, September 28 as part Purple Flag Week.
The week is celebrating the Purple Flag Award - an accreditation scheme for excellence in night-time economies, similar to the Blue Flag for beaches.
It runs from this Saturday until next Saturday and will also include a tidy-up of Halifax town centre on Tuesday and safety advice being offered in The Woolshops from 12pm on Monday.
The work done by Halifax Street Angels helped Halifax win the Purple Flag Award.
One of the angels, Ellis King, said: “We often work with young people aged 18 to 24, who have had too much to drink and become sick or collapsed in the street.
“We take them to our safe place cafe where we clean them up, give them any first aid they may need, reassure them and their friends they will be okay and we continue this until they are in a state where they are able to get a taxi home.
“We offer support to anyone that has been injured. We have qualified first aiders on each of our teams and they will either clean up someone who has been injured, give them advice on how they can avoid potentially dangerous situations and we observe any incidents which look like they could escalate or become more dangerous and will try to get the police to them before they do.”