You could use a bluish filter.

Bart

Try for example an 80A filter or similar.

Shoot raw and boost the blue in the raw conversion process?

Set the white ballance while shooting toward a yellow card?

You have probably inadverently set an incorrect whitebalance -
maybe to 'cloudy' and you are shooting indoors or something
like that. I don't know Nikons, but there should be a way
to change it - either to automatic, or matching the type
of the environment you are in (daylight, tungsten, ...).

If this happens with the automatical white balance, the camera
is probably faulty (and the filters are not going to change
the results).

Regards

Color balance.

Thanks a lot for everybody's reply. Unfortunately I am still not able to do
what I intended.

1) I first took a picture of a white paper with "Direct Sunlight" setting.
This corresponds to a color temperature of 5200K.

2) I checked the RGB values.  Red had the maximum gain and blue had the least.

3) Then I changed the white balance to "Incandescent" which corresponds to a
color temperature of 2700K
I checked the RGB vlaues for this setting. I could increase the Blue by an
appreciable amount. The gain of each of the colors was almost equal.

4) Now I took my actual subject, which is a Candle flame. But with this
subject, and a setting of 2700K color temperature the gain on blue was again
the least. Any ideas how I could improve the gain so that the R, G, and B
gains are almost equal. I am using NIKON D100. I know we could use a blue
filter, but I was curious to know if it is possible to do it by just playing
around with the settings on D100 NIKON.

Thanks,

~Jay