Fifty Shades of Grey
Mathematica, 30 bytes

Here is another Mathematica approach:

ArrayPlot[#+5#2&amp;~Array~{5,10}]




or

ArrayPlot[5#+#2&amp;~Array~{10,5}]




The first one simply creates an array

{{6, 11, 16, 21, 26, 31, 36, 41, 46, 51}, 
 {7, 12, 17, 22, 27, 32, 37, 42, 47, 52}, 
 {8, 13, 18, 23, 28, 33, 38, 43, 48, 53}, 
 {9, 14, 19, 24, 29, 34, 39, 44, 49, 54}, 
 {10, 15, 20, 25, 30, 35, 40, 45, 50, 55}}


and the second one

{{6, 7, 8, 9, 10},
 {11, 12, 13, 14, 15},
 {16, 17, 18, 19, 20},
 {21, 22, 23, 24, 25},
 {26, 27, 28, 29, 30},
 {31, 32, 33, 34, 35},
 {36, 37, 38, 39, 40},
 {41, 42, 43, 44, 45},
 {46, 47, 48, 49, 50},
 {51, 52, 53, 54, 55}}


Then, ArrayPlot plots them as a grid and, by default, uses greyscale to visualise the values.