In recent years we have been building tunable, narrow band, birefringent filters for the visible spectrum. These filters have bandpasses as narrow as 50 mÅ and can be tuned anywhere in the range 4500-7500 Å in less than one second. They operate over temperature ranges of more than 50°C with wavelength stability better than 5 mÅ. Wavelength stability and control are achieved by reference to a HeNe laser and precision temperature sensors under the control of a microprocessor system which tunes the filter to compensate for temperature variations. The microprocessor capability combined with some new ideas on birefringent filter construction can now enable even more flexibility and active contol of filter performance. Continuous control of passband width as well as location is possible. Real-time control of the shape of the entire visible spectral band for color balancing is now possible.