How do I manipulate descendants in this case?

local descendants = script.Parent:GetDescendants()
 
for index, descendant in pairs(descendants) do
	if descendant.Name == "Grass" and descendant.Touched == true then
		descendant.BrickColor = BrickColor.new("Bright green")
	end
end

I wanna make all of the descendants of a model the color "Bright green" when touched by the player. I am probably using .Touched wrong but this was the only way I thought of and yeah... It's not working.

You have to connect a function to the touched event that changes the color (for each descendant that is named "Grass").

Here is an example:

local descendants = script.Parent:GetDescendants()

for _, descendant in pairs(descendants) do 
	--[[
		we aren't using index, so let's 
		just replace it with "_" a Lua convention
		for naming things we don't use.
	--]]
	if descendant.Name == "Grass" then
		local connection
		connection = descendant.Touched:Connect(function(hit)
			if hit.Parent:FindFirstChild("Humanoid") then -- making sure it's a player touching
				descendant.BrickColor = BrickColor.new("Bright green")
				--[[
					Unless you wish otherwise, I don't see
					why you would want this touched event
					to fire other than the first time the player 
					touches the grass, so I'll disconnect the event
					once it is fired once.
				--]]
				connection:Disconnect()
			end
		end)
	end
end

We can't use descendant.Touched:Wait() because that would yield the script until the event happened, and the loop would not finish. ####I hope this helps! Have a great day scripting.

More on...

• :Disconnect()

• :Wait()

• BasePart.Touched

• Detecting if a player is touching

Touched is an event, not a property. Events use the Connect function to establish another function to be called whenever the event is fired.

You need to use the Connect function to make a Touched event for descendant. Note that you must check if the object that hit was a player. This can be done by checking for a Humanoid, since all Character's have this object.

local descendants = script.Parent:GetDescendants()

for index, descendant in pairs(descendants) do
	if descendant.Name == "Grass" then
		--Connect function to Touched event, 'h' is object that hit
		descendant.Touched:Connect(function(h)
			--Make sure it was a player
			local plr = h.Parent:FindFirstChild("Humanoid")
			if plr then
				--Configure BrickColor
				descendant.BrickColor = BrickColor.new("Bright green")
			end
		end)
	end
end

Happy developing!

Righty. Sorry to slap you with a script right off the bat:

--I'd advise the script to be in ServerScriptStorage but here it is as normal:

tChildren = script.Parent:GetDescendants()

function COLOR(ColorSelect)
for _,z in pairs (tChildren) do
if z:IsA("BasePart") and z.BrickColor ~= ColorSelect then z.BrickColor = BrickColor.new(ColorSelect)
end end

script.Parent.Touched:Connect(COLOR("Bright green")

This is going to do the following:

A) Lookup children A.K.A descendants

B) Use a Touched event to turn them Bright Green and wala!

If you have something to say don't be shy, we're a team now.