I use the Image Gallery a lot on my website (wargamersterrain.com). The ‘little’ arrows are hard to see and I find to way to change them. I’ve numerous comments from customers asking if the arrows can be made into large ‘chevron white’ (or something like that) so it’s easier to see.
I agree with my customers, the arrows are hard to see, even of I change the color they are still too small.
Joe
Yes Joe they are a bit on the small side. At this stage there is no way to change it but it has been mentioned several times to the Sparkle Team and I’m sure it is on their to-do-list! 
Hi !
Well, it is possible, but it would require manually modifying the page’s source code. I would advise against this as it could potentially cause issues on the page, but if you want me to explain how to do it, you can send me a private message. Also, please note that if you modify the site on Sparkle and republish it, it will erase the modifications and you will need to redo the changes manually.
Alternatively, there is a second solution: replicating a gallery system with popups and larger arrows. It is a lengthy process, but it is possible.