Microsoft Excel - Why are some dates greyed out in my excel calendar?

For example......in this calendar for May 2015, the previous months dates (that overlap in May's calendar) are greyed out.  Also, in column G, rows 8 and 10, I have included a formula to (cell G8) add one day from the last work day in the previous month and (cell G10) subtract a day from the last work day in the previous month, however, the number is greyed out.  Try as I might, I cannot get the text adjusted so that it isn't greyed out.

Thanks for taking the time to look into this for me.

Thanks,

Kathy

 I tried to paste the spreadsheet here, however, it would not allow me stating inappropriate content was found.

I hope you are able to help without the visual.

Thanks,

Kathy

Hello Kathy,
This is a fairly standard convention for calendar layouts.  I assume you have obtained the code for the calendar from somewhere and there is probably somewhere in the code that firstly changes the formatting of the cells not relevant to the current month and then protects them from being changed.  So I would think that you would have to work through the code and find the relevant part and change that appropriately.
If you want to attach a file you have to zip it and use the left hand icon at the top of the edit window to upload it.
Regards
Harry