Voters said they were confused over the similar shade of orange used for the two papers - one to elect their constituency MP and one to elect a party-list MP.

"The similar colour of the two papers confused me and my neighbours. We didn't know which paper we had to put into which box," one villager in Chon Buri said.

In Amnat Charoen, complaints over the colour confusion were made through a national radio programme broadcast in the area.

Among the highest-profile voters to complain was Democrat Party vice chairman Suthas Ngernmuen

"Obviously, something strange has been done by the EC in this election. Things are confusing, even to the election officials at the polling stations. They cannot explain why this is so confusing," Suthas said.

"An investigation is needed into this [ballot colour] scheme," he said.

Amnat Charoen Governor Suraphol Phongthadsirikul admitted that the similar colour of the ballots was possibly confusing for voters.

He said he had asked the provincial EC officer to explain the difference to voters at polling stations.

At a polling station in Uthai Thani, security guards were asked to explain the matter to the public.

An officer at the EC's headquarters in Bangkok explained that it was not the EC's intention to issue similar coloured ballots.

"The EC in Bangkok set general guidelines that the party-list MP ballots would be of the same colour in all electoral regions, which this year is orange.

"Then, for the constituency MP ballots, we gave each electoral region a choice of five different colours. Unfortunately, some regions chose a shade of orange similar to the party-list ballot."

Sumalee Suwanakorn,

Kwanjai Bootboonkaew

The Nation