Recently I had a requirement to modify a calendar control which looks like below.
Requirement:
Requirement was to create a home page for employee attendance regularization application which shows a calendar.
calendar control should display employee's attendance data( In/out time) for selected month.
Achievable tasks:
1. background color using
calendar.toggleDatesType([ "2013/04/12" ], sap.me.CalendarEventType.Type07, true);
2. meaning of colors using CALENDAR LEGEND.
Challenge :
1. Custom labels below the dates
Calendar control ( sap.m.Calendar ) does not have such property (as per my knowledge) to set the labels on / after dates.
Using extend() method we can extend existing control and give some new properties and aggregation and all.
As per the link extend TreeNode in SAPUI5 the function renderInnerAttribures is a specific hook of the TextFieldRenderer. As it is not supported for Tree, I found that it is also not supported for calendar.
So as shown in above link i also used the onAfterrRendering() method of sap.ui.core.Control and customized my Calendar as below.
code:
calendar = new sap.me.Calendar({ dayHeight:80, monthsPerRow : 1, currentDate : "2013/04/30", });
calendar.onAfterRendering = function(oEvent) { var divs = $('.sapMeCalendarMonthDays').children(); var i; var length = divs.length; var classes; for(i=0;i<length;i++) { classes = $(divs[i]).attr('class'); $(divs[i]).append('<br/><span style="width:100%;display:block;font-size:0.5em;font-weight:bold; color:green">In:10:30</span><span style="width:100%;display:block;font-size:0.5em;font-weight:bold; color:green">Out:06:30</span>');
//check the condition
if(i==3) $(divs[i]).addClass('sapMeCalendarType04');
if(i==11) $(divs[i]).addClass('sapMeCalendarType07'); } };out put.
This document was generated from the following discussion: Calendar control modification
Please provide your inputs if i am wrong somewhere or missing something 
Happy Learning
Below are few links for reference.
Documentation/AdvancedTopics/OnTheFlyControlDefinition – SAPUI5 Wiki (TIP CORE User Interface)
Documentation/AdvancedTopics/OnTheFlyControlExample – SAPUI5 Wiki (TIP CORE User Interface)
Documentation/AdvancedTopics/CompositeControl – SAPUI5 Wiki (TIP CORE User Interface)