Google Apps Spreadsheet Script for Coloring a cell based on the value it contains, if it's a hex color.

Colorizer.gs

function colorize() {
  var rows = SpreadsheetApp.getActiveRange();
  var numRows = rows.getNumRows();
  var values = rows.getValues();

  for (var r = 0; r < numRows; r++) {
    var row = values[r];
    for (var c = 0; c < row.length; c++) {
      var val = row[c];
      
      if (val == '' || val == '#') {
        continue;
      }
      else {
        if (val.indexOf('#') === 0 && val.length === 7) {
          rows.getCell(r + 1, c + 1).setBackground(val);
        }
      }
    }
  }
};

function onOpen() {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{
    name : "Colorize Selected",
    functionName : "colorize"
  }];
  spreadsheet.addMenu("Script Menu", entries);
};