The PKR de facto leader pointed out that Sang Saka Malaya was part of the nation's history.
"Sang Saka (Malaya), according to these youth's interpretation, should be introduced because this is also one of... the flags that was proposed by those who had fought for the nation (pejuang-pejuang bangsa)," Anwar told reporters. "What's wrong with the younger generation knowing history, knowing Sang Saka?"
Leaders from the ruling Barisan Nasional (BN) coalition had alleged that Pakatan Rakyat (PR) intended to change the country's national flag, a claim the opposition pact immediately denied.
Anwar also pointed out that Umno's party flag was originally named Sang Saka Bangsa.
Earlier, a blogger had admitted to waving the "alternative" flag together with his friend at Dataran Merdeka last Thursday, but said it was intended to educate the public about the nation's history.
In his attempt to shed light on the controversy, the blogger identified only as Singa Selatan said that the two of them "do not represent any political party" and "clearly have no motive to change the Jalur Gemilang to Sang Saka Malaya."
According to the blogger, the Sang Saka Malaya - which sports a crescent moon and an 11-pointed star in the top left corner of the flag against a two-striped red and white background - was used by the first Malay party, Kesatuan Melayu Malaya (KMM) formed in 1938, that had fought against the colonial British for the country's independence.
"That is why I feel that this flag is qualified to be flown on the night of the independence (celebration) apart from Jalur Gemilang.
There are many tales full of hardship behind the Sang Saka Malaya," he said in the blog.
He also said he was stunned to see copies of a pamphlet calling for the Jalur Gemilang to be replaced with the Sang Saka Malaya and denied responsibility for its distribution.
The police said that they are investigating an alleged proposal to replace the Jalur Gemilang national flag under the Sedition Act, despite Putrajaya's decision to repeal the controversial law that has been widely panned as a tool to curb political dissent.