An advert for a skin-whitening cream that appeared to offer university scholarships to students with fairer skin has stoked a debate over racism in Thailand, where Unilever – the company behind the ad – has been forced to apologise for any "misunderstandings".

The "Citra search for clear, soft and glowing skin" asked female students to submit photographs of themselves in their university uniform along with a bottle of Citra Pearly White UV body lotion, for a reward of 100,000 baht (£2,000). Citra is a Thai subsidiary of Unilever.

The advert – broadcast on Thai TV and YouTube – showed two female students, one lighter-skinned and another darker-skinned, who were asked what could make them "outstanding in uniform".

The darker-skinned girl seemed incapable of answering, while the fairer one – whom presenters described as "beautiful" – said Citra products could help.

The advert sparked a debate over skin tone and education levels. Many believed the inference to be that darker-skinned students are less intelligent than their lighter-skinned colleagues in a country where fairer skin has long been equated with higher class – as a whiter complexion suggests a life not spent toiling on a farm.

Although the advert was withdrawn last week the scholarship competition still stands. Contestants have a chance to enter until 31 October and their skin will be judged on "product efficacy", with winners allowed to spend the funds as they choose.

Skin-whitening products abound in Thailand, as they do all over south-east Asia, with pale models advertising cosmetics, pills and diet supplements to lighten dark complexions.

Products promise "the miracle of white skin" at the same time that common Thai insults use darker skin as a subject of denigration, like dam mhuen e-ga, "black like a crow".

Much of the debate over the Citra advert raged online in popular forums such as Pantip.com, where users questioned why a skin-whitening product should even be related to a university scholarship.

"Now you can get a scholarship because of white skin – not because of good studying, not if you are poor and dark," user MyOwnDream was quoted as saying in the Bangkok Post.

Unilever Thai Trading said it never intended "to suggest racial discrimination" and apologised for "any misunderstandings regarding the campaign".

It said: "The Citra brand will exercise greater sensitivity for brand activation campaigns that take place in the future."

Thailand is no stranger to race-based controversy. In September, a Dunkin' Donuts ad had to be withdrawn after human rights groups complained about a model in blackface makeup advertising a "charcoal donut", while in May an advert for a skin-whitening drink that featured a brown bear, a black doctor and a Thai woman in blackface was also deemed racially insensitive.