How to get value from multimap based on condition?

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C++14

Hi, I am storing key-value pair in Multimap (I have duplicate keys and values, so I'm using multimap).
I need to iterate every key and corresponding key's value, then return the value if both key and value match the condition. How can I achieve this using multimap?

Example:

Key - Value
a - Red
b - Green
c - Red
a - Blue

From this above key-value pair, I need to return above value for the corresponding key if both key and value match the condition.

I need to do like this,

MyKey = a
MyValue = Blue

if(MyKey==Key && MyValue==Value )
{
// Return map value.
}

What I have tried:

I need to do like this,

MyKey = a
MyValue = Blue

if(MyKey==Key && MyValue==Value )
{
// Return map value.
}