If you're running the Windows version, in Celestia v1.6.1 you can
Open the menu Render --> View Options...
In the Grids section at the right side of the menu,
Select both Ecliptic and Galactic
The Ecliptic and Glactic grid colors are very similar. The Galactic grid is pale yellow, while the Ecliptic grid is pale pink. You can toggle them on and off while watching Celestia's window to make sure you know which is which.
While the View Options menu is still open (so you can toggle the grids if necessary), you can select Celestia's main menu and change its viewpoint appropriately until you locate where their planes intersect. Numeric values for some of the grid lines are shown along the edge of Celestia's window.
I believe the Mac and Linux versions are similar.
Below is a screengrab showing what it looks like on my computer with Equatorial, Ecliptic and Galactic grids shown. It gets a little busy