Elizabeth,
a factor which as not been mentioned so far is reciprocicity failure. Most color
films will give acceptable color reproduction if the exposure is within a
defined time period. If the time period is exceeded then there is a color shift.
This is because the sensitivity of the three colors in the emulsion is more or
less equal within that time period but varies outside those limits. Some
exposure systems can correct somewhat for this.
For immunofluorescence studies whether the color is apple green or a more
yellowish may not be very important unless quantitation is required.
If the lamp voltage is too low you will also get a background that is more
yellowish than white. It is important to set the lamp at the setting for the
correct color temperature.If the light intensity has to be decreased do so with
neutral density filters which decrease light intensity without changing the
color balance, make sure that these are truly neutral density filters.
As already mentioned, use of correct filter to correct color if using a daylight
film.
Barry