manual stated mixture of dark green and standard green.the standard
green I suppose can be subsitute with tamya NAO green.
But do anyone knew knew the right color for the conqueror?or right mixture.

For the period of Conqueror's service the colour of British AFVs was Deep Bronze Green; I still occasionally use enamels and have found that the Revell (Enamel) Colour 65 with a coat of gloss varnish works very well.

It can always be toned down with filters/washes depending on the ultimate portrayal of your model.

However, there is plenty of documentary evidence that these tanks were also finished in a matt paint; what shade exactly I do not know. Conceivably it could have been due to the crews dulling the paint down themselves.

Humbrol 163 is an exact match for British Army post-war green. They do it enamel and acrylic.