If it's full coverage, it shouldn't matter too much. Just decide what color, if you could see a tiny bit of it behind stitching, would look the best. Do you do railroading and/or laying? Those two things help cover. And sometimes I find that using smaller count doesn't cover as well as 14 count, if using two strands. The lower count Aida sometimes allows the stitches to lay flatter. (I have three full counts in progress now, and the one on 14 is covered just as well as the 18 count one.) Hope this helps. Love the picture you're doing!

Hi Lab!
If this is a full coverage project I would say it doesn’t matter, BUT I won’t say that. When I look to beginning any type of project to choose a fabric, I always look at the LIGHTEST colors in the pattern to assist me in deciding the color of the fabric to purchase. Why? Because I don’t want any show through from the fabric color.
In your project I would go with the ‘oatmeal’ color or maybe an ‘off-white’ material.
Another strong suggestion, make sure you get good coverage with your floss! Nothing like stitching away and finding out your getting show-through of your fabric. If this pattern’s instructions state to use 2 strands of floss, save yourself a lot of grief and do a row 5-7 full cross stitches on the border of your fabric with 2 strands of floss, THEN do a row with 3 strands of floss below the first row and compare which coverage you like better. Five minutes of doing a floss ‘coverage test’ will save you grief from seeing fabric show-through. Hope this helps! 😊
A beautiful project for you to stitch your first cover-all on!

Thanks for your suggestions. I had to do a search for "railroading" as I wasn't sure what that was, so evidently I haven't been doing this. I'm fairly new to cross stitch. Great suggestion for a test row for coverage and I will order the oatmeal. My son proposed to my daughter in law on top of this lighthouse so this will be a gift for them (if I live long enough) ha ha.

I like to ‘railroad’ but on some projects, ‘no can do’ because I’m using an odd number of floss strands, Love doing it on two strands.
What a beautiful gift for them as a lovely reminder of the day of engagement!
Feel free to ask questions. There are a LOT of Counted cross stitchers on this ‘chat’ with varying degrees of experience. We enjoy helping others.....😊

Bermuda, great concept regarding the lightest color and show thru. I'm gonna try and remember that hint!

lab1110, what a wonderful remembrance this project will be for the couple. Congrats.

Thanks MarzHere,
What made me think of it was from looking at a pattern I bought (Virgin Mary kissing the infant Jesus, ‘Kissing the face of God’ at Scarlet Quince website).which has very dark dark browns in the background which I considered just buying a very dark brown fabric, BUT ( there’s always a ‘but’) ....
There are very light creams, whites in Mary’s clothes and her face, etc. and I was worried about a very dark brown showing through the white, off-white, light cream colors of the floss.