CASH-strapped Translink spent more than £30,000 on rainbow makeovers for rail and bus services during the coronavirus crisis.
The spending came despite Translink warning of a £100 million funding shortfall amid lockdown prompting a collapse in passenger numbers.
A public spending lobby group criticised the public transport firm's rainbow designs as an "unnecessary splash of paint".
But Translink said it delivered "important messages of safety, hope and solidarity".
Rainbows became a symbol of support for key workers during the pandemic, with many households displaying rainbow colours and drawings in their windows.
Two trains were given rainbow makeovers as part of Translink's 'chase the rainbow' initiative.
Designs were also displayed in bus shelters and advertising space, and children were asked to submit their own rainbow drawings.
In total, £15,720 was spent on the rainbow wraps for two trains, £11,920.05 for adshells and buses, and £2,550 on digital assets for press and social media.
Translink however refused to disclose the project's marketing agency and consultancy costs.
Citing a 'commercial interests' exemption, it said releasing this would breach its contractual agreement with the PR agency involved.
In April, Translink said it would need a £100m injection of funds to continue providing a public transport network across Northern Ireland after the coronavirus crisis.
In February before the pandemic escalated, a senior civil servant warned a Stormont committee that Translink's viability was "in jeopardy" and while it had managed to maintain the rail and bus network by drawing on its reserves, it was "running out of options".
Jeremy Hutton, policy analyst at the TaxPayers' Alliance, branded the rainbow scheme an "unnecessary splash of paint" given that Translink's finances "were in a poor state before the recent crisis".
"Translink needs to reassess its priorities and spend money where it is needed most to stop the organisation going off the rails completely," he said.
Translink said the rainbow initiative was well-received.
It said rainbow designs were featured on 110 buses and almost 300 bus shelters and advertising space, with the latter provided free of charge by external advertisers.
"This creative rainbow campaign delivered important messages of safety, hope and solidarity during the Covid-19 emergency," a spokeswoman said.
"Translink recognised this was not an easy time for the nation and as a leading responsible organisation, wanted to play our part in serving the community to support the wider government campaign and also support the important message of mental health and wellbeing by letting people know they are not alone at this difficult time."
