Why aren't text and image buttons responding?

I am making a shop gui for my game using filtering enabled, however when I move my mouse over the button in studio the button does not respond, it just stays white.

Here's my local script:

local OpenGui = game:GetService('ReplicatedStorage').Remote.GuiOpen

script.Parent.MouseButton1Click:Connect(function()
	OpenGui:FireServer('shopMainFrame')
end)

And my server scipt:

function openGui(player, gui)
	game.Players:WaitForChild(player.name).PlayerGui.Guis.ScreenGui:WaitForChild(gui).Visible = not game.Players:WaitForChild(player.name).PlayerGui.Guis.ScreenGui:WaitForChild(gui).Visible
end

game:GetService('ReplicatedStorage').Remote.GuiOpen.OnServerEvent:Connect(function(player, gui)
	openGui(player, gui)
end)

My StarterGui looks like this:
https://imgur.com/a/nZpIt

And here is what my guis look like when the mouse is over them: https://imgur.com/SVUrGS0

Do your images have transparent backgrounds? When Roblox darkens your button on mouse hover it is actually the background that is getting darker, not the image. So if your images are opaque the color change will not be visible behind the image. To fix this, either use images with transparency, or if you cant/don't want to then you can use something like this to get the same effect:

local button = script.Parent
local defaultButtonColor = button.ImageColor3
local hoverButtonColor = Color3.new(0.8, 0.8, 0.8)

button.MouseEnter:connect(function()
	button.ImageColor3 = hoverButtonColor
end)

button.MouseLeave:connect(function()
	button.ImageColor3 = defaultButtonColor
end)

Server Scripts cannot access PlayerGuis, only LocalScripts.

LocalScript

local guiHere -- Location of  the gui that you want to open

script.Parent.MouseButton1Click:Connect(function()     
	guiHere.Visible = not guiHere.Visible
end)