The field is green, with the coat of arms in the centre. The coat of arms was given to the city by Charles III, King of Navarre, in 1423. Description: a silver lion in a blue field, with a red bordure with the arms of Navarre – gold chains on a red field – and the [open] royal crown on the top. We know that there was a green flag [already] in 1512. A white and blue flag was used at some times in the 19th and 20th centuries; but the use of the green flag was decided again in 1930.
Miguel Izu, 14 Jun 2000
The city flag had many variants in the 19th century. According to Banderas no.4:
In the middle ages it was green;
In 1830 appeared a white over blue flag with centred arms;
In 1915 a ceremonial white flag with arms is created but the white over blue flag continues as normal flag. The reverse of the ceremonial flag was green with a green (sic) crown of thorns with a white centre and five red wounds (I never saw it, I do not know how is possible a green crown on a green field, so I assume that crown of thorns is bordered white);
A report dated June 1923 confirms the green flag and says "...la bandera sustituida era blanca con jirones azules y las armas de la ciudad..." ("the former flag was white with blue gyrons and the city arms"). Green [is said] to be adopted because the first two known flags were green (first book of the [Pamplona?] regiment dated 1559/1560). The white ceremonial flag was also moved to green [sic].
On 1st October 1923 a newly appointed (conservative) City Council prposed the adoption of a white flag. A report was requested to Juan Carlos Guerra who answered 4th June 1924 proposing a light blue flag based in the
Privilegio (privilege) of King Charles of Navarre of 1423, and suggesting that the old 'green' flags were in fact decoloured blue flags.
On 24th August 1924 was readopted once more the white ceremonial flag with arms and the white over blue flag without arms.
On 5th June 1930 a newly appointed (liberal) City Council changed the flag to a green one with arms which should be the current one.
The reverse did not change after 1915.
Sources: Banderas no. 4, letter from the Pamplona City Council dated 19th May 1924, report from Mr. Guerra, Mondragon 4th June 1924.