Firstly, when printing with VC paper I do not believe that the use of cyan fitration is capable of helping you at all. Of course, this may well indicate that once again am I mentally constipated. Try this: make a satisfactory exposure with your magenta and yellow. Dial in the mamximum cyan as an addition to your current filtration. Make a second exposure, Woo, that surely made a difference ania?
So what color might help? Red? Maybe. but it will be rather strong medicine.
A light red such as a cc50R could be useable. Neutral density is preferable.
Where to put it? Well, I can think of three spots. It has been a longtime since I have owned a V35...like 25years. If you can open your mixing box easily then put a polyestedr ND filter inside. If you like 15-20 second exposures then use an ND .9 3 stops of light decrease. This will put the rather fragile polyester filter where it will stay pristine. Second choice tape it to the top of your diffuser on the negative carrier but the filter will be subject to scratching etc. which may cause no harm but is, I feel, certain to cause no improvement. Thirdly, I do not recall if the 40mm Focotar has filter threads on the front. If it does get a high quality glass MC ND filter of the appropriate strenght and screw it into place,...UMMM make that 4 choices remove your red filter and replace it with an ND filter..again use a glass filter that is MC and of high quality.
If a 2 stop correction will do the job, and you already own a polarizer then the polariser in any orientation into the light beam...YAh, Yah, Yah I already know that a polarizer has a standard filter factor of 2.5x but it has a neutral density that is extremely close to .6.
The V35 is, I feel, a wonderfully elegant enlarger. It is so handy to use. My ownly regret is that Leitz did not offer it with the 50mm Focotar II and appropriate cam. For myself I would glady settle for a reduction in maximum print size and an increase in optical quality were I to own a V35.
Enjoy your enlarger.