In the capital, Bogota, families of victims were given white flowers by well-wishers to symbolise peace.
The agreement, reached after years of negotiation, was rejected by a slim majority in a national referendum earlier this month.
Campaigners for the "No" vote have demanded a series of changes.
Farc leader Timoleon Rodriguez, better known as Timochenko, said on Wednesday he was confident the deal could be revived although he said he would be reluctant to re-negotiate some elements of the accord.