Working on adding TokenURI

contracts/ColorMinter.sol

@@ -9,6 +9,7 @@ import "../node_modules/@openzeppelin/contracts/token/ERC721/extensions/ERC721En
  */
 
 // Charge a few in order to mint a token
+// Set Token URI w/ IPFS metadata
 contract ColorMinter is ERC721Enumerable {
     // The token ID that will be given to new minted tokens.
     uint256 private _tokenId;
@@ -25,13 +26,14 @@ contract ColorMinter is ERC721Enumerable {
 
     // Ex: "#21F32"
     // Mints a new token based on a HEX color.
-    function mint(string memory _color) public {
-        // Must accept only HEX colors
+    function mint(string memory _color) internal returns (uint256) {
+        require(msg.value == 1e12, "Amount sent must be 1e12.");
         require(!_colorExists[_color], "NFT already exists!");
         _safeMint(msg.sender, _tokenId);
         _colorExists[_color] = true;
         _tokenValue[_tokenId] = _color;
         _tokenId++;
+        return _tokenId - 1;
     }
 
     // The total amount of tokens that have been minted.

contracts/Exchange.sol

@@ -3,7 +3,6 @@ pragma solidity ^0.8.0;
 
 import "../node_modules/@openzeppelin/contracts/access/Ownable.sol";
 import "../node_modules/@openzeppelin/contracts/token/ERC721/utils/ERC721Holder.sol";
-import "../node_modules/@openzeppelin/contracts/utils/math/SafeMath.sol";
 import "./ColorMinter.sol";
 
 /**
@@ -15,8 +14,6 @@ import "./ColorMinter.sol";
  */
 
 contract Exchange is Ownable, ColorMinter, ERC721Holder {
-    using SafeMath for uint256;
-
     receive() external payable {}
 
     fallback() external payable {}
@@ -54,6 +51,11 @@ contract Exchange is Ownable, ColorMinter, ERC721Holder {
         return _tokenInfo[_tokenId];
     }
 
+    function mintNFT(string memory _tokenUri) public payable {
+        uint256 tokenId = mint(_tokenUri);
+        // _setTokenURI(tokenId, _tokenUri); //Needs to set tokenURI
+    }
+
     /**
      * @dev Allows a user to sell their NFT to the DEX and also specify
      * their sell price in wei. Checks to make sure the sell price is greater or equal
@@ -128,7 +130,7 @@ contract Exchange is Ownable, ColorMinter, ERC721Holder {
         address _tokenOwner,
         uint256 _tokenSalePrice
     ) private {
-        uint256 payAmount = _tokenSalePrice.sub(1e12);
+        uint256 payAmount = _tokenSalePrice - 1e12;
         (bool success, ) = _tokenOwner.call{value: payAmount}("");
         require(success, "Transaction failed.");
     }